Oh yea you're going to get a lot of opinions on this question. First off these engine weights are with their factory supplied manifolds.
340-525#, 383-400=620 and 440=670
Keep in mind you can shed a lot of weight off the BB's by going to aluminum intake, aluminum water pump, headers and since you're looking at strokers aluminum heads.
Personally I've driven both A body SB's and own a A body BB and for the life of me I don't feel much of a difference, now I've lightened mine up further with a fiberglass hood so maybe I'm not making a fair comparison. But hey I just don't see any difference in the handling, maybe if I was racing it on a track I would and that's JMO.
Terry