Thanks for all the replies! I knew this was the place to ask this question.
I knew the aluminum head (L-78??) 396 was close in weight to the SB, but I didn't think about lightening the motor with the other aluminum goodies.
I doubt I'll go with headers, because I don't like the sound of my 68 convertible with a small block and headers (guess I'm getting old). The 69 is also a ragtop, so if I go with the BB, I'll probably run manifolds.
Looks like I may be keeping the BB, and buying a 12-bolt (car has an 8.2 10-bolt now). I have an M-20 with the car, so maybe I'll just put that whole combo in and see if I like it.
Time will tell, I guess.