My brother built a rotisserie for his son's 69 Roadrunner body out of two engine stands from Harbor Freight. Use square tubing or angle iron to connect the bases together firmly, and fabricate a cradle of some type to secure the cab to the rotating head assemblies. Be very careful to design the holding brackets in such a way that the cab isn't top-heavy in one direction. You should have it balanced where its own weight will keep it steady no matter where you turn the assembly. That's going to require that the pivot points are placed about halfway between the floor and the roof, with brackets fabricated to reach the original cab mounts under the floor.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
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