I'm on a roll with these updates...
Does not buckle under a load and the sheet metal is fastened to the wood with countersunk screws. Should be adequate for welding and for any other heavy work that I can think!
They found their place in my "Leaning Tower of Compressors".
When I bolt the rotisserie to the floor, I will be able to level the car perfectly and also pull the car straight if need be. Now the car is level to a sound of few degrees.
Fortunately the cross measurement of the car was spot on... at least the car is not fully crooked!
Unfortunately I need to lift the car with engine crane to be able to adjust the threaded rods, but that's quite easy! Just lift the car, check levelling and adjust the bottom nuts to correct height. Lower the car and tighten top nuts.
Same for the front and rear!
On next update work resumes with patch panels and more precisely rocker panels!