Gen 1 Gen 2 parts interchange question

I'm curious as to what parts interchange. I have a 68 Handibus Custom 108" that will be my driver. My donor is a 64 90" G10 panel. It looks like the doors are a straight swap and maybe even the side barn doors are the same as the rear doors on all of them. The 64 doors are in better shape all around and don't have those ugly side markers. I know springs are different but it appears the 64 may already have gen 2 springs. For spares I might just keep the rear end and front axle as well.
I will try to get around to posting the 64 parts in the for sale section when I get closer to knowing what I keep and what goes. I already have the bumpers promised to one of the members here who I also need to get back to.

Hello hermeytheelf, how is that 64 gas tank. I'm in need of a tank for my 68. I know it's a smaller tank then the 68 has, but if your maybe looking to let go and everything lines up I might take that off your hands. I will wait to hear back from you before I look into this further. Thanks for your time.

The door assemblies are interchangeable,,,,,,but the inside parts are not,,,,,,,the 1st gen has 2" wide springs,,,,,the 2nd Gen has 3" springs  and get weirdly down to 2 1/2"  to squeeze through the U bolts......front axles are not interchangeable,,,,,,,

Yeah, other than some sheetmetal there really is not to much that is a direct or correct bolt on between the 1st and 2nd Gens. A lot of almosts and looks likes.
68mancave , you probably will have better luck trying to find a good 2nd gen tank. Good 1st gens are scarce and the mounting to put in a "smaller "tank doesn't seem worth it to me.

a 22 gallon 3rd gen chevy tank is very close to the second gens,
the filler neck is further toward the rear of the tank, and the sender
that goes in it will work with the second gen gauge.

Thanks everyone for the replies and info. Twinpilot001 may have one for me in a few months so I'm keeping my fingers crossed until then.