Well the nomads and classics have different tank mounts, fuel pumps, tank bezels etc. The frames are very different too. As far as I know there's nothing that is swappable and I've been trying to find something for 2 years. I was hoping gmanindustries was going to come out with their extended range tank but they had too much trouble with the fuel injection systems because of our in-tank pumps. They only offer it for carb'd classics.
My plan would be to have a similar tank but 3 lines: vent, fuel up, and fuel dow.n
Unfortunately it means I'd need 2 pumps and I have to weld onto the stock tank for 3 bungs.
It should work fine but they couldn't do it that way because of the welding to your stock tank. It also gets a bit more expensive with 2 micro fuel pumps. I want to do it that way though because injected vehicles can be fickle about fuel pressure so I want to retain the stock pump to do the actual feeding of the engine. Otherwise you risk trouble lights and rough running. I also trust the stock pump more than something aftermarket. So this way if one of the 2 micro pumps fail my stock pump and range are fully intact.