I think it's common to assemble the front suspension on the frame before lowering the body. That's what I did, at least. I also red loktite'ed the lower pivot in the frame. I considered drilling a hole and tapping it for a set screw for tightening the nuts for the A-arms, but didn't. I'm taking the lower A-arms off to measure them. I assumed all my A-arms were straight because I knew their history and they didn't look bent in the least. One day in a paranoid frame of mind, I had checked the caster on the driver's side to make sure I had assembled everything correctly - I had - so I didn't pay attention to the passenger side till much later. It turns out the caster on the passenger side is off. Now, I'm taking the lower A-arms off the passenger side (I have tubular adjustable A-arms at the top and there is now way they are bent) and I find that I'll have to do some grinding on the body or the pivot or both to take the rear A-arm off!
I have a few suggestions for those of you who are doing body off restorations. They really apply when you are using new lower pivots such as if you have a new frame:
1. Assemble the suspension after the body is lowered to the frame so you can adjust the position of the pivot before you lock it down.
2. Consider drilling and tapping a hole in the tube for the lower pivot for a set screw. This should be accompanied with grinding a flat in the pivot that is an inch or so long. This will allow you to adjust the final position of the pivot (of course, if you do this, it can be done before you lower the body!). If you take this route, anti-seize or grease on the pivot would keep it from getting rusted into the frame. At some point, you may want to take it out.
2a. Another possible option is to weld a nut on one end of the pivot and then install the pivot from the front. I think this is best done after the body is mated to the frame to ensure proper clearances.
3. Probably most importantly, if you use stock A-arms (I recommend this since they are designed to absorb a lot of the energy in an accident helping to save your frame), measure them first before assembling everything. Don't trust the way they look. Before I started taking it apart, I put a straight edge on three sides of both arms and the only thing I could find was a very slight bowing on the vertical side - no deformations on the horizontal sides.
I hope this helps somebody.
edit: added option 2a.