Good update Kevin
You should definitely get a Marti report. I think they are about $50. My buddy just got one for a 74 Bronco he just got and it has great info on it. All the build options and even where it was delivered to. That is an interesting question about the reproduction VIN plate. I guess since your car is already titled you won't really be getting any scrutiny on the VIN # but I would have some concerns about putting a non original one on there and the potential can of worms that could open up. Maybe no big deal though. Just something to think about.

I have seen some 911 builders doing the frame powder coat thing. Looks like a great option. I have learned about all sorts of different ideas from following other builders on instagram. Maybe you could find some useful accounts there. Wonder if the extra thickness although minimal causes any issues on reassembly? I know I had to chase some of it out of the holes on the Cobra frame.
I don't really see the benefit to keeping the old doors unless it is drastically cheaper. The car will be nowhere near an original example when finished so repo doors are no issue and would save you the trouble.

Is your exterior vision for this car still a work in progress? You mention the chrome trim possibly needing some work. Does blacking out the trim appeal to you? I am thinking the same thing on my project car and will look into the process and cost for blacked out trim. Seems like a little more modern look but chrome looks great also.

Are you considering IRS out of the wrecked Mustang as well?
This is gonna be fun. We can spend all sorts of your money on this one!