Ever the contrarian, I'll say this- the factory threw (and in many cases this is the correct descriptor) it all together at one time. It's doesn't make it impossible and it may, actually be an aid in certain cases. Most of us have realized that the factory gaps were and are a joke. My car, before it got cut up, had gaps under the doors between the rocker, that you could slide your fingers under. Having said that, the opportunity to take your time and fit the panels as nicely as possible, is there when you start from scratch. You have to look at it as a giant, metal jigsaw puzzle. The other gentlemen are correct advising the car to be on it's suspension, as that's the way the car will carry it's load and if you build-in stress by welding it up when not in the position it wants to normally be in, you'll regret it. You've got the diff in it, so I'd support it in the frt where the Kmember resides as well. Here's the great secret of doing bodywork- if it doesn't fit; why doesn't it fit and what do you need to do to make it fit- period. Spending hours trying to put the sheet metal equivalent of 10lbs of $hit in a 5 lb bag is not only expensive, it's infuriating. Hang the panels- all of them- and see how your gaps go. You appear to have the lock plrs still in it, so your options regarding door/qrtr gaps are finite unless you want to move them. See the previous comment about that. I'd re-hang the doors and fndrs and see how they go; if they're within spec, hang the 1/4's and see what you've got. Watch your body lines since while the doors can move up and down; the 1/4's won't move much. If you can get a good fndr/door/qtr alignment and gap, pin them in place and see how the whlhses go in. Remember to stick the rear floor in before you finally hang the 1/4! Ain't bodywork fun?! Enjoy.