I have not yet voted becuase I see this as an unfair comparison. The SB you offer seems to be a better matched combination that what you are considering for the Bb 433 cu in package. If SB I suggest to get some revvs.
Normally I would have selected the BB 433 but you have tied it down with component choices beginning with the heads. The LS6 Closed Chamber Heads are not the best in the world.
Convertor will be pretty good for the BB.
Convertor change might workl better for the SB.
Your choices of cylinder heads is putting a head on the SB that is far better than your BB choice. The SB could maybe benefit with more cam and some good rpm.
If you are talking the 1971 LS 6 Open Chamber heads the story changes quickly.
Just opinions, not really knowing more about cam or other things.
Suggest to try just using regular headers and swap sides and turn them upside down to find what you want.
Ed