I wish I was just that far along. I do have a stock 350 Chevy sitting on a stand. For now I'm just watching everyone else for ideas. Good luck on your build up.
Redrilling rotors to 5 on 4.5 is no problem. What was the issues with the calipers? pistions, seals, brake pads materials have come along way since then.
Some is using the GM front wheel drive cars like the 80 through 84 "plus or minus a coupe of years" rear brakes. Cars are Eldorado, Buick Riveria, Olds Tornodo.
Soak them with some PB Blaster. There is some better penetrents out there, just can not remember their name. Also smack the bolt heads with a hammer or with a center punch. Don't damage the edges.