I can't say which is best. Once I built mine, I didn't pay close attention to their construction at shows, though I have seen a few nicely constructed ones first hand. I have seen various heavier designs supporting a lot of weight in demonstrations. I don't think that's highly important. The unibody for the Firebird is somewhere around 600-800 pounds according to what I've read. All of these should easily handle that. A sturdier design would be best if you contemplate taking it to a media blaster on a roll-back. One of the more important features is the type and diameter of the wheels. A small diameter hard wheel will stop dead in it's tracks when you try to roll it over a pebble. Any of these commercial designs will full adjustment for balance would have good resale value when you're finished with it.
I think that trying to leave the glass installed would defeat the purpose of a frame-off restoration. It would be like fixing a rain stained ceiling in your house without repairing the leaking roof. These cars fail, in part, because of primer and lacquer failing underneath the glass seal. A little rust in there turns into advanced rust, leaking, water soaking on the carpets and under the trunk mats. Soon you have rotten floors trunk pans and trunk drop-offs. All the rust in my project started with the glass support channel paint failure. I really don't think you can skip this step unless someone had done this area over using modern paint, "glass out" before.
I took everything off. Glass, doors, front frame, quarter glass and heater plenum, interior etc before placing the body onto the stand. It's necessary to reduce the weight your dealing with. After all, you'll be turning the car on it's side to work on it. You don't want 3200 pounds spinning on gimbles and turned by hand. It's also necessary to remove the parts in order to keep media grit out of all the parts.
