Converting my Pontiac wagon to a stick. Pontiac doesn't technically make a BB. But it's a 400, physically the same size as a 455. I grabbed all stock components manual components from a 79 Grand am. G body cars used a 4 speed saginaw. Not really made to handle BB power. The problem you will have is the shifter location on a saginaw is much further forward than a Muncie or Super T10 (I am using). So unless you can custom create a shifter some how it will be in the middle of your bench seat or if you go to buckets, you can't use a factory console. (it won't fit)
I guess after being half through my install I would suggest going with the LT1 6 speed set-up or even a TKO600 if funds are available. And make use of the hydraulic clutch linkage. The only thing you'll really re-use is the pedals. I had the Super T10 and I upgraded to an iron case and Nascar style mid-plate. Should be good to 600 ft/lbs now. But I have no overdrive. I guess I could always add a gear vender's unit if I want down the line. The 4 speed in-line shifter has been a b*tch to fit and requires custom linkage and top-plate for the console. I still don't know how it will turn out.
In short use the saginaw and stick with SB power or be prepared to spend $ for buckets and the appropriate hardware for a manual transmission that will hold up to BB power.