This post is request for guidance since I now need to learn how to fabricate an entire tub.

Here's the back story:

I originally intended to replace the firewall, floor pan, and trunk pan. That plan quickly eroded when I identified backyard hackage throughout the car. Now it appears the only original metal will be the rear sear frame. I'll limit the finding list to bondo, 3/4" thick, sheet metal screws, rivets, and house grade silicone. The typical bad scenario. This car was also hit in the T-bone area (back seat window) on both sides.

Experience and confidence level: high

Current status:

Frame rails, trunk pan, floor pan, and firewall removed. What does that mean? The alignment points are missing.

Parts on hand:
Door and rear quarter frame / full rockers (pic below), trunk pan, floor pan, firewall, frame rails, full rear quarters, rear inner and outer tail panels, (on order: cowl, cowl shoulders).

First question:

Where's the starting point?
1. Build a jig and restore from the frame rails, and interior pans up?
2. Replace the door frame, rear quarter frame on each side and then pot it on a jig?

Second Question:
Are all metal seams supposed to be even or do the seams vary in depth (ie.. Floor pan to rockers)

Third question:
Can I fabricate (weld) the truck pan to the floor pan or will doing so cause a misalignment risk?
1. Is the one piece front to back floor pan measurement provided on the vendor websites accurate?

Appreciate all guidance provided!

Wade