Great offer to take JAFO up on Jamie! If he wrote all that down, it'll save you a lot of figuring and factoring. Until at least to the point you figure out yours is different from his by 1/4" in every dimension! Then you'd just need to "compensate" for the inconsistencies of these things.
Man Jamie, yours and the others that posted their gems look like someone actually intended to flip them by covering stuff up. I can't imagine too many reasons for that much Bondo on the interior!
In your case I know you already have the fender off. You're doing great work for a "first timer" at least for this level of diggin'inta.
I mentioned bracing in your other thread, and again here. Even though you've got your frame for support and alignment, don't trust it 100%. Do what you need to, especially if you go for the full panel.
A perfect example of not trusting the frame is when we pull the transfer case crossmember out, many times it does not go right back in without some real English because as soon as it was unbolted, the frame sprung in our out. No lie, sometimes they literally pop when you get that first bolt out!
That's when you learn that "conditions are fluid" until the last weld is made.
Sometimes the bit-by-bit approach is beneficial. Sometimes the full monty is the way to go.
It does save you some welding time, but you really have to bracebracebracebrace if you're going to cut the entire center of the truck out all at once.
I don't have any specific advice or instructioning for you at the moment. You're into it pretty far, and doing a great job all on your own. You have the first-hand view of what's really going on with your rig.
This is more of a support group for therapy when the stress gets to be too much!
Drinking can still be involved of course, but the group sessions reduce the instance of hair pulling and being committed to a hospital.
Again... Having fun yet?;D
Paul