Here are a few ways to make the rotisserie a bit more stable.
1) Pivot Point In the front is higher so the car is better balanced. You can roll it through 360 degrees and not an issue to get it back upright.
2) All of those 2 x 6's build out the rotisserie pivot point so the frame rails do not interfere with the front of the engine stand. Now attaching directly to the frame rails also solves that problem, But car needs to be attached further away up front
3) Removing the center leg allows the rotisserie pivot point to be at 90 degrees from floor. Otherwise difficult to get ot to an angle where it rotates easily in the pivot point
4) Bigger wheels increase floor clearance as well as 2 " 4 bolted to front cross member increases height off of floor
5) Electrical conduit was used to stabilize and keep both ends of the rotisseries aligned. I simply flattened the ends in the vise and used a big lag bolt to attach to a piece if the 2 x 4 extension for the wheels
6) one pair of wheels swivels and has locks on casters.
7) Initially putting on the rotisserie the ends looked like /----\ I used a ratchet strap to pull the ends in so car was then sitting like |----| and then added the 12' 2 x 4 in the center to hold everything together.
8) I have a chain hoist I used to pick up the rear that runs to an overhead beam and front can be picked up by 4-5 Grandsons, they had to work for Thanksgiving dinner or engine crane can pick up the front. I leave the chain hoist attached when car is on it's side and I am working on it. A little tension on the chain vastly increases stability when I am whailing and flailing on the Body of Bugsy.
9) Wheels came from Harbor Freight in Rear and Tractor Supply in Front. U Bolts Tractor Supply.
10) Conduit only comes 10' lengths. coupler is required. Do not count on pressure on coupler screws to hold things together . I put things together then drilled holes through the screw holes on the coupler into the conduit itself and then screwed screws all of the way in. Physical lock instead of just a friction locking screw.