I have ran a M20 & M21 behind my 250 and I leave the line no less then 5000.Only Broke the 29 splined axles.And I have run both these same tranny's behind a BB 396/(bored to a 427)Anyway
my 64SS chevyII with a 250 has 15x15.5x29s & 5:13 gears under it An NO less then 5000rpm Off the line. Watch the video's and see for yourself.

Larry/Twisted6
[oooooo] smile
Adding CFM adds boost smile
shocked God doesn't like ugly.