First off, I commend you for taking the trip to Fordville. Secondly, I want to add my 2 cents.
I think you should go '84, You already mentioned the paint, And I am sure a straight body and nice clean paint job will sufice you fine. You just don't see that many built nicely 84's around anymore.
Motor: With the power you wish to acheive your options seem to be pretty clear...BIG POWER, and longevity(at least enough to drive to cruise spots).
I don't know what you have/want to spend on a block, but a strong foundation is really the way to start. My idea is to look into a new Dart block, or possibly a A351 or R351 block.
You mentioned you want big CI's, but also what boost range do you plan to run? If you run 400+ you won't need to run major boost to make big power. That will come with a well built big CI motor.
Maybe a nice 404 or 410 CI motor with a 83mm turbo, or a F1 series Pro Charger blower. (intercooled or not).
Tranny: I can't really foresee a manual tran's with that much torque and HP. So an Auto will probably be the way to go. Maybe a Super strong C-4 , or if you don't mind the weight a C-6. Or even a Powerglide, with a streetable convertor.
Rear: As for a rear why not build a 8.8 BUILT, or a 9inch and use a coilover style setup to keep things adjustable yet streetable. You can still Mini tub, or use a Ladder bar rear to go straight.
Interior: It has been done full interior with a race car, but think about it, if you buy a early style car to save weight why no keep things minimal in the cockpit. You can still retain stock style seats or even some less exspensive Sparco or Corbeau seats have a clean stock apearance yet save weight.
Wheels, Tires, and Paint, that is the easy stuff.
But I always did say...*Build a street car that will survive at the track, Not a track car that can survive on the street.*
I'd like to stay updated on your progress, Do you have a website, or are you thinking about making one to host your project?