Homemade version. YES!
Looking at the basic way the set I picked up is made. A car jack came to mind(effecitvely all the parts would be there* short of a couple bars).
I just slapped these together. I have some ideas on how I could mount them to a bench. I will still use wax paper to avoid sticking. I will also probably add cork to the top and back bars(protect softer woods). I will also place a long block at the sides for better pressure spread. Even as is though these would do solid bodies just fine, and can be adjusted down for necks or what have you.
As far as steel over wood for the cross bars. I have steel that could be bolted up, but there just is no reason to use it unless I wanted to use 4-10'bars to span the clamps. I would probably still use cork on the bars to protect the wood.
Peace,Rich
Car jacks was the first thing that i thought of too!
Great minds eh