There are several rotisserie designs used. One has a giant wheel on each end while most use what look like adapted engine stands. Back in the '90s, Ted Mitchell built his own rotisserie to successfully restore both his L and his son's pushbutton Panteras.
Ted included the plans and dimensions in a POCA Newsletter article (available free in the POCA Archives), if you're poor and handy in the garage. He said nothing beats doing underbody work standing up or sitting, instead of laying under a constant shower of debris or welding sparks.