This is a comprehensive list of parts from other bikes (or unique/creative mods) that will directly (or w/ minor modification) fit on 1st generation Z1K's ('03-'06). What do you know or have tried on yours? I will add to this list as the inputs come in. 
**The listing you see on this FIRST post is current as of post #164!
SUSPENSION / STEERING
Forks
- 03-08 ZX6R
Mods Required: None, the triple clamps are the same.
- 06-07 ZX10
You have to press z1000 stem into ZX10 2006-07 lower triple. Check the following link for help: http://www.riderforums.com/showthread.php?t=41243
** 2004-2007 ZX10 forks are okay.
** 2008 ZX10 forks are too long.
Shocks
- 03-05 ZX6R
Mods Required: The '05 636 shock will NOT directly bolt in. The lower legs on the 636 shock are 2mm closer together, and there is a spacer inside the shock linkage which will not fit into it. Need to have 1mm milled out of the inside of each shock leg to get it to bolt in.
- '05 ZX10R
Mods Required: I've personally got one, just haven't installed it yet. Mods TBD...
- 01-04 GSXR600
Mods Required: Minor clearance probs, slightly too short
Swingarm
- 98-02 ZX6, ZX9, and ZX12
Dog Bones
- ZX9 or ZX6
Mods Required: None required
BRAKES
Rotors
- ZX10R Wave Rotors - fronts DO NOT fit, the mounting holes are offset
- z1000(03-06), ZX12R(05-07), and ZR-7S(03-05) front brake rotors are all the same
**Additional info from DynaGrego:
Z1000 03-06 can use 320 original rotors from the following Kawasaki models.
ZX 7 '91-'03,ZX-9R NINJA '94-'97,ZX-9R NINJA '02-'03,ZX 1100 '93-'01,ZZR 1100 '93-'01,ZZR 1200 '02-'05,ZX-12 R '00-'03,VN 1500 MEAN STREAK '02-'03,VN 1600 MEAN STREAK '04.
Mods Required: None

Master Cylinder
**Info from DrRipper:
"FYI, 05 zx6 master cylinder bore is 16mm, 09 zx-14 radial 11/16" (17mm), 08 triumph daytona radial 3/4" (19mm). Daytona master has the banjo coming out more towards the back and obstruct the throttle cable slightly (rotate right side switch housing slightly to clear the banjo). ZX14 is better. daytona nipple (for reservoir) is from the side, 90degree upwards, while zx14 is from the top, 90degree pointing sideway. Those who are picky about reservoir placement for aesthetic reasons will want to consider these small issues."
Calipers
- 2001-2003 GSXR 600/750/1000 calipers
Mods Required: May require creative brake line routing or longer hoses
More info, courtesy Dynagrego:
SIX POT CALIPER from GSXR1000 K2! (longer hoses required)

OEM CALIPER.

:glassestiCOMPARE.

COMPARE AGAIN(BOTTOMS)

Compare pads.

Another setup, courtesy Dynagrego:
"Calipers from ZX10 2008-2010 is a direct swap when using forks from ZX6R.They are better than older radial calipers because they are using 2 pads instead of 4. I have also installed a pair of 320mm rotors and I can't believe how strong the front brake is now."
The parts you are going to need are:
1)Four long caliper bolts Μ10 Χ 70mm Χ 1.25 from yamaha R1 2004-2008.
2)Four common spacers for M10 bolts,2mm thick(photo).
3)Longer hoses.
Kawasaki also uses these calipers on the new 2011 ZX10. They must be good.
WHEELS
- Rear
2000-2003 ZX9
- Front
1998-2002 ZX6
2000-2002 ZX9
ENGINE PARTS
ZX-9
- Cams ('98-'03)
Mods Required: There's a few things required for this. Here's a great thread on it:
http://www.riderforums.com/showthread.php?t=40581
- Flywheel / Stator / Cover ('98-'03)
Mods Required: Requires lengthening the wires by about 5-6 inches.
**will drop approx. 2 lbs. of rotating mass
DRIVELINE
JT Sprockets
Front JTF1537.16 (Same as '04 ZX10 16 tooth)
Rear JTR1489.42 (Same as '04 ZX10 42 tooth)
Renthal (courtesy of Parts411)
Front 1212-0036-pu $36 or someone mentioned 400-525-16P
Rear R184U-525-42-HA-pu $56
Sprocket Specialists
Front 572S-16
Rear 706-42
EXHAUST
2001 ZX9R header
Modification required: Collector hits rear shock, needs to be slash cut and flipped 180 degrees.
D&D
Mods Required: Fab new hanger
FUEL INJECTION / INDUCTION
Pod Filters, K&N Part #RC-1064
Mod Required: Airbox removal
BODY
Tail Components
- ZX6R
Mods Required: None
MISC PIECES
Clutch lever & Perch
- Almost any Kawasaki cable clutch & perch will fit
Rear Sets
I saw someone with a set of modified aftermarket ZX10 rearsets on their bike once. If you know who it was have them post up here on how they did it...
GAUGES
2005-2006 ZX636 gauges are a direct bolt-on. Main difference is that the RPM range will be different and the 636 does NOT have a fuel gauge.
**The listing you see on this FIRST post is current as of post #164!
SUSPENSION / STEERING
Forks
- 03-08 ZX6R
Mods Required: None, the triple clamps are the same.
- 06-07 ZX10
You have to press z1000 stem into ZX10 2006-07 lower triple. Check the following link for help: http://www.riderforums.com/showthread.php?t=41243
** 2004-2007 ZX10 forks are okay.
** 2008 ZX10 forks are too long.
Shocks
- 03-05 ZX6R
Mods Required: The '05 636 shock will NOT directly bolt in. The lower legs on the 636 shock are 2mm closer together, and there is a spacer inside the shock linkage which will not fit into it. Need to have 1mm milled out of the inside of each shock leg to get it to bolt in.
- '05 ZX10R
Mods Required: I've personally got one, just haven't installed it yet. Mods TBD...
- 01-04 GSXR600
Mods Required: Minor clearance probs, slightly too short
Swingarm
- 98-02 ZX6, ZX9, and ZX12
Dog Bones
- ZX9 or ZX6
Mods Required: None required
BRAKES
Rotors
- ZX10R Wave Rotors - fronts DO NOT fit, the mounting holes are offset
- z1000(03-06), ZX12R(05-07), and ZR-7S(03-05) front brake rotors are all the same
**Additional info from DynaGrego:
Z1000 03-06 can use 320 original rotors from the following Kawasaki models.
ZX 7 '91-'03,ZX-9R NINJA '94-'97,ZX-9R NINJA '02-'03,ZX 1100 '93-'01,ZZR 1100 '93-'01,ZZR 1200 '02-'05,ZX-12 R '00-'03,VN 1500 MEAN STREAK '02-'03,VN 1600 MEAN STREAK '04.
Mods Required: None

Master Cylinder
**Info from DrRipper:
"FYI, 05 zx6 master cylinder bore is 16mm, 09 zx-14 radial 11/16" (17mm), 08 triumph daytona radial 3/4" (19mm). Daytona master has the banjo coming out more towards the back and obstruct the throttle cable slightly (rotate right side switch housing slightly to clear the banjo). ZX14 is better. daytona nipple (for reservoir) is from the side, 90degree upwards, while zx14 is from the top, 90degree pointing sideway. Those who are picky about reservoir placement for aesthetic reasons will want to consider these small issues."
Calipers
- 2001-2003 GSXR 600/750/1000 calipers
Mods Required: May require creative brake line routing or longer hoses
More info, courtesy Dynagrego:
SIX POT CALIPER from GSXR1000 K2! (longer hoses required)

OEM CALIPER.

:glassestiCOMPARE.

COMPARE AGAIN(BOTTOMS)

Compare pads.


Another setup, courtesy Dynagrego:
"Calipers from ZX10 2008-2010 is a direct swap when using forks from ZX6R.They are better than older radial calipers because they are using 2 pads instead of 4. I have also installed a pair of 320mm rotors and I can't believe how strong the front brake is now."

The parts you are going to need are:
1)Four long caliper bolts Μ10 Χ 70mm Χ 1.25 from yamaha R1 2004-2008.
2)Four common spacers for M10 bolts,2mm thick(photo).
3)Longer hoses.
Kawasaki also uses these calipers on the new 2011 ZX10. They must be good.

WHEELS
- Rear
2000-2003 ZX9
- Front
1998-2002 ZX6
2000-2002 ZX9
ENGINE PARTS
ZX-9
- Cams ('98-'03)
Mods Required: There's a few things required for this. Here's a great thread on it:
http://www.riderforums.com/showthread.php?t=40581
- Flywheel / Stator / Cover ('98-'03)
Mods Required: Requires lengthening the wires by about 5-6 inches.
**will drop approx. 2 lbs. of rotating mass
DRIVELINE
JT Sprockets
Front JTF1537.16 (Same as '04 ZX10 16 tooth)
Rear JTR1489.42 (Same as '04 ZX10 42 tooth)
Renthal (courtesy of Parts411)
Front 1212-0036-pu $36 or someone mentioned 400-525-16P
Rear R184U-525-42-HA-pu $56
Sprocket Specialists
Front 572S-16
Rear 706-42
EXHAUST
2001 ZX9R header
Modification required: Collector hits rear shock, needs to be slash cut and flipped 180 degrees.
D&D
Mods Required: Fab new hanger
FUEL INJECTION / INDUCTION
Pod Filters, K&N Part #RC-1064
Mod Required: Airbox removal
BODY
Tail Components
- ZX6R
Mods Required: None
MISC PIECES
Clutch lever & Perch
- Almost any Kawasaki cable clutch & perch will fit
Rear Sets
I saw someone with a set of modified aftermarket ZX10 rearsets on their bike once. If you know who it was have them post up here on how they did it...
GAUGES
2005-2006 ZX636 gauges are a direct bolt-on. Main difference is that the RPM range will be different and the 636 does NOT have a fuel gauge.