In my younger days I decided to repaint in Bolero red rather than the factory Butternut, also switched out the interior from black to red. That was the 80s. Looking back, I wished I stayed with the original color. Prefer the red but it's not correct. Just my 2 cents, it's your car and choice. Many will see a black car and immediately suspect it is not factory correct, then proceed to pick the entire car apart. I think you'd get more, and the right kind of attention with the correct SF color.
Whatever you do, keep/rebuild all your original parts before modifying anything, think twice before throwing out old parts and document with a lot of pictures. I'd be torn if the owner of the other car turned up here. There was a nice thread over at Team Camaro about a guy who bought a T-bucket, realized it had an 67 MO block and later sold it at little or no profit to the guy who had found as was restoring that rare car. A little different situation here, and if that car is still around the owner might not even be interested. And I know it's not always easy finding a numbers and date correct engine. Some say if it's not the born-with motor is doesnt matter what is under the hood, but personally I feel if you have something date and numbers correct, with a close VIN, it adds more value than something out of left field. I'm not sure if the tranny numbers change much. There seems to be less concern over p-glide correct numbers than Muncies.
If you have time, post up some pics of the trim tag, body etc. May help others in offering their views. Photobucket is a good site to host pics.