You mentioned a 'chassis' in post #1. Do you have a body over chassis (a la Bolwell, Elan, etc) or a unibody vehicle?
Engine stands have load ratings but I'm guessing two x 2000 lbs stand would take whatever you have otherwise how are you going to get it on to the rotisserie! I used 1000 lb stands and inserted a 300mm extension into the vertical post, that gave me ground clearance and cleared the fluro lights on an 8' ceiling.
If you can mount off the suspension points then its shouldn't flex. I don't really have any good photos to illustrate but the 'legs' of the adaptors at the front ran along the main rails on my project
(edit - 240Z). I wince when I see folks fixing adaptors to the bumper mounts.
