before 83? DAMN, i hate you... we in California have to look for Pre-73 vehicles.
Ok, the myth of running open headers.
It will sound cool!... but will decrease low end pull... only performance gain it'll give you is higher end pull. And we know most street races, and track races live in hte low RPMs so it wouldnt help you out except attract attention from the local athorities.
Hmm Nitrous motor... forged internals would be the best idea. A 4-bolt main block would be a good idea as well.
As for having a smog except car, welcome to the club! haha... ummm its hard to say what parts to use... High rise manifolds... umm 750cfm+ 4bbl carbs.. big tube headers... free flowing mufflers. all these things are up to you, what you want to do to the car is your choice. it'll be a fun car regardless what you do.
Just remember, you're car is only as fast as your driveline. Spend as much time thinking the rest of the driveline as you do the Motor. a 500hp motor wont do you much good if you blow up the transmission, twist the drive shaft, and blow up the rear end you're first run.
Stock transmissions, and rear ends are not an option. You'll need to look up aftermarket parts.
B&M Transmissions and their accesories can be found at places like
http://www.bmracing.com
Eaton Posi's can be found at...
http://www.drivetrain.com/eatonposi.html