Yes, indeed, those are engine stands - Harbor Freight, and I think about $50-60 each on sale. The only modification is to remove (don't install) the wheels on the legs and instead use a 2x2 board (to get the rotational axis horizontal). I make no claim for this design - I got the ideas from others posts on VAF.
Here are the modified stands:
Here is the firewall mount and stand (2x4s, deck screws, engine mount holes and some custom shaping to fit the outer skins):
Here is the tail mount off and on stand (a custom fitted 2x4 bolted to the tail/fuselage bulkhead, more 2x4, deck screws). Note: this first attempt shown without the stand did NOT work.
Look at this second picture closely - an additional 2x4 has been added to lower the rotational axis below the bottom of the fuselage at the tail:
The key is to have the center of rotation at each end aligned and in the right place to maintain rough balance (not too top heavy), yet high enough to clear the stand and floor. The HF stands have pins to lock the rotation so that even though the balance is not perfect, you can secure at 45 and 90 degree rotations.
I would go through the effort of a rotisserie again - it was worth it. YMMV