big block stall behind a small block

Problem is nobody can give you an answer with the limited information.

As other posters have stated, the HP/tq of the engine is going to play a huge part in stall speed. Say that converter stalled 3500 behind a tired mid 70, 240 hp BB and you put it behind a 450hp, 450tq 360. No way that converter stalls at a lower rpm than when behind the BB.

If it's a hughes, part number is either 24-35 or a 27-35 IIRC One is a 904 number other is a 727. They are written on with what looks like a black sharpie and should be red in color.

I've had good luck with Hughes converters the 2500-3500 shelf stuff. A true 3500 converter would be a good piece behind that SB you have. If a 528 mechanical, that cam kicks butt.