The wonderful thing about an early z is they are very light. 400-500 lbs stripped I did not stress too much over alot of things for this first try, because the margin for error is so large. The other thing about a rotisserie is you should never need to be under the car, so there is very little chance of me getting hurt.
I took 2 harbor freight 750# engine stands. I cut them with a Milwalkee Port a Band about half way up. I bought some 4x1/4x24" plate at lowe's and I had some tubing at the house. I raised the rotating hub to about 48 or so inches off the floor to make sure a larger car had room to spin. I bought some casters from harbor freight so I can roll into the yard for media blasting or load it on a trailer if neccessary. I had an old rectangular trampoline frame that some one gave me and I cut that up to make the attachment bars and to brace the stands. I also welded up a tube that runs from stand to stand. I welded 1/2x13 nuts on the top of the stand's front leg centered over a hole for bolts to hold the stand togethor.
When I welded things up I leveled the forward leg with a bottle jack I clamped things togethor and leveled the hub with a torpedo level. I also plumbed the vertical scab plates with the level.
I filled the space between the plates with some 1 1/2 x 1/2 thin wall tube I had laying around. The brackets for the car have a round 2" tube. I used muffler clamps 2 on each end. I would raise one end tighten the clamps, then raise the other. I will eventually make a threaded rod adjuster that can raise the car using an impact wrench. I designed a rotisserie on my computer but after steel got so expensive I had to improvise. Wheels, wleding wire and all I have about $350 in this one not counting the trampoline frame.
The balance point for the car is 2-3" above the center line of the bumpers. I will say this, I used tube to come end where the front bumper brackets mount. I used 60mm bolts 10mmx1.25 (i think) to mount those to the car. They are pretty sturdy. The back bumper mounts on the car flex alot more and I will probably fab a bracket that can be added to mount to the diff bolts to help with the load.
Wow... that got long. There is more detail than that but ask questions so I don't ramble anymore.