SHEET METAL WELDING ORDER

You have a lot to do there,
Remove quarters
remove wheel houses
remove trunk pan & extensions
remove rear valance

Then mock everything up
Wheel houses
trunk pan & extensions
rear quarters

Then remove and mock up rockers
Screw everything in place do not weld, make sure everything is lined up where you want it
Leave the doors on make sure alignment of rear quarters are good.
if you are satisfied with the placement of everything then start welding in
Make sure the the car is supported on jack stands and level.

after you're done with the rear section move onto the front
Cowel & inner fenders