six pack intake question

There are two "series" of big block, "B" & "RB".

B engine are the ones with 3.375" stroke: 361, 383, 400

RB engines are the ones with 3.75" stroke: 413, 426 Wedge, 440


The RB engines are a bit taller and have a slightly wider intake manifolds (about 1") than the B engines.