[Dominik]

By the time you are ready to fit the body your son will be old enough to help...

The CSX 4000 and Kirkham bodies have different support frames. You would have to cut that frame off with the body and weld the new one on. Kirkham once supplied ally bodies including the support frame.

Pic shows a CSX 4000 chassis. For starters, the ally body has more supports in the door areas and a different scuttle frame which holds the door locks.

However, on a more home builder oriented Cobra, like a RAM or a Contemporary where the body, boot insert and passenger tub is ONE piece, you can lift it off.

After you stripped dozens of items.

And obviously the wheelbase must be the same.