Dave, thanks

Personally i would put the car on 4 even jackstands and do my work(brace then replace), after being on the rotisserie. It can be leveld pretty good that way.

Here is how my 70 GTX looks in the WORST possible position. Yes it flexed a LOT with the wheel cans removed but before the quarters and rockers were removed. We leveled the car on jack stands ,then removed the 1/4's, rockers, and pillar posts.
The replacement 1/4,rocker,pillar assemblys which were removed from a donor car went right on and fit with very minor effort. My next step will be to hang the doors from rebuilt hinges to make sure of alignment then I will finish welding all the holes. The pieces are welded and screwed (temporary) enough for clearance of doors at the moment.

Pic 2
Lots of work but it is at least looking like a car again!

The trunk lid lined up fine.

Another view

Sounds like a plan. Looks like your GTX is coming along nicely. Thanks for the pics, looks like it shouldn't be a problem.