For the "thin" version (80 GB, 120 GB, or new 160 GB), they should be interchangeable. There is a slight RPM difference, but it should still work. I do not have them available, or else I would test it to know for sure.
The LCD has a different width ribbon cable, but you mentioned switching out the ribbon cables. I've never tried this, so I'm not sure if you can pull it off...can't say one way or the other on that one.
Additionally, you can swap front cases between the two, and of course the button is interchangeable. I haven't tried the click wheel yet. These iPods are very touchy with the click wheel. If the cable is slightly off, the iPod will not start.
I hope this gets you started!