Believe it or not, I used to work for the inventor/developer/manufacturer of those "Topsiders" , they were called "Tuneup Hoists" when we made and sold them in his small plant in Manteca California back in the late 50's after I got out of the Army - that was where I learned to weld. They were designed from different materials then, and looked a bit different than what we see now - but worked the same.
GM finally bought him out, dunno what or whether they ever did with production of the hoists themselves, the inventor was Linus Snyder, long since dead - but was talking with his son Gary - my age now - a few months back, and he says he still holds the original patent on the hoists - surprised GM didn't get that as well...