You don't need a rebuild if it only has 20 thousand miles on it, just get your rear main seal fix , radiator take care of and any other leaks. Then put your cam, heads and other mods on and go have fun.
Just a quick couple of questions for you how many miles do you have on the motor right now and are you burning a little or a lot of oil? If your burning oil its probably time for a rebuild. Depending if you need rebuild or not your machine shop should tell you if the motor needs to be bored or...
Can't wait to see this build come together. My closest friend had a couple 390's when he was younger, he said it was nasty motors he ever had. They use to do a lot of street racing back in 60's and early 70's.
We don't hate you. That's the only thing about putting a different motor in a different car, it can be costly especially modifying parts. Cutting into the firewall might be one way to go but then your going have to modify your drive shaft, but thats cheaper than dry sump pump system. If you cut...
If your going to put a newer modular motor in it, then you should use a newer transmission and rear end. I would also upgrade the front end suspension and steering. If your going to run and fuel injection, then your going to need wiring upgrade.