When I was a much younger version of myself, I had an idea of doing a modification to my '65 similar to what you have there, just on the stock C20 frame. So basically lengthen the cab and shorten the bed. I am glad I didn't do it. Seeing yours, I don't like the look. It is a nice truck, and it's different, and it has it's cool-factor to it. The door handles and rear fuel door are a nice touch. To me, it just doesn't look right with the xtra-cab and 6 foot bed. I think it is because it sits so low that my eye disagrees with it. 4x4 height of a '64 four wheel drive truck, to me, would look a lot better.
It's good you found a shop that could diagnose the problems with the transmission and ECM.
I have a feeling I may run into a similar situation when I go to get mine painted. I want a simple single-stage paint as well, and each panel will have already been removed, cleaned, rust preventative added, and reinstalled. The "outer shell" will only need some prep and be shot with color, nothing fancy. I hope I can find a shop that will agree to do that type of paint job. Basically the truck will be completely painted everywhere else when it goes to a shop.