What sheet metal to start installing first?

[mr48chev]

I'd think it is kind of similar to building a house. You do the foundation and get it square and then build off it.

You might have to build down from the top in your case though as it seems that you don't have a lot there to attach to if you go bottom up.

Personally I'd get the hinge pocket in place. set the doors on and make positive that the door gaps are right where you want them and adjust the bracing accordingly and then put the rockers in and probably do the floor and floor bracing and work my way up from there.

I learned a lot of things when I chopped my truck or since I chopped it and one is that it is imperative to get the door gaps perfect before you start on the rest of it.
The second thing is to have patience and don't get caught up in the "I have to do x amount of the work today or else" as that quickly creates issues that you have to go back and correct or you will always know are there.
Last when it becomes "work" instead of creating and fun back off and go do something else unrelated to the truck. Take your lady for a ride or a date night, go fishing or dig the clubs out and play pasture pool or anything else that totally clears your head of issues on the truck and then with a clear head you can go back and it should be back to creating and having and enjoyable time.
As long as you can see positive progress on a regular basis it doesn't matter how much progress just that you are making progress.

[OrrieG]

Originally Posted by mr48chev

play pasture pool

Ok, I'll bite, what is pasture pool, pocket pool with the bulls???? Swimming in the horse tank??

On the core support shims, that can be affected by the cab angle alignment too, which also affects the bed. Before final welding get the doors with the step sill parallel with the frame at the right height, probably stock shims with yours. Then the core support and hood and fenders in that order. There are lots of threads about hood alignment that go back to doing the fenders and core first and the hood not fiting. On TF the fenders align with the doors. I would also drop the bed back on to make sure the horizontal accent lines are lining up. Now and then I see a truck where lots of work was done on the front clip and cab but the bed is tilted because there was not enough room to shim it to align with the cab/door line.