I pulled my taillight panel then the trunk pan & drop-offs. Then I welded a cross-beam between the frame rails just ahead of the rear cross member before removing and replacing the rear cross-member. After that, I replaced the trunk pan and drop-offs. Then, I replaced the taillight panel, but didn't reattach to the quarters. Next came the quarters and outer wheel houses (did each side separately). My logic was that having something major attached while doing each area would help maintain the integrity of the car's unibody - which I was honestly waiting for the whole thing to collapse once I pulled the taillight panel... it didn't.
Was this cross-beam the thing you mentioned in your build as the "gas tank hammock"? If my cross member is in good enough shape and I can leave that will I still need this cross-beam temporarily between the frame rails?
Exactly right. I used it because it was the most handy piece of metal I had laying around at the time that would fit all the way across. Since the rear frame rails were going to be separated from pretty much everything at the rear end, I figured I'd at least give them a little bit of support (from each other) while I replaced the rear cross member. If your cross member is good, you won't need the extra bracing - I just used it for peace of mind while having it all apart.
BTW - the gas tank hammock was not actually part of my build, but rather a Redneck Engineered solution to keep the gas tank in the car since the previous owners had let the trunk pan rust out so badly it fell apart (since the forward bracket for the gas tank straps welded directly to the underside of the trunk pan, after all).
As I found it, once I started pulling loose trunk pan sheet metal from the car:
While employed as a support bracket while I replaced the rear cross-member:
Rear cross-member replaced:
While I had it all open, I treated the insides of the frame rails with Rust Bullet Black Shell (epoxy primer):
Make sure to get the 'long' trunk pan, not the short one like I did:
Since mine's a restomod and I'd already bought the short panel (not knowing there was a difference), I just made a panel to bridge the gap:
Just after removing and replacing that rusted out quarter extension panel (whatever it's called - seen in the other pics):
After that, welded in the new taillight panel:
And test-fitted everything to see that I'd gotten it all lined up:
After that, I started in on the quarters.
Hope this helps!