5.9 Mag stock LB or rebuilt SB
I got a 68 Valiant Signet, with a 380 hp crate (400 hp) with 727 & 2800 rpm stall and 2.xx:1 gears, works pretty good still fun in the street it's a little hard to get up into the power band cause of the highway gears, it's still got plenty of power at lower rpms but if I really want to get up in the power band, I need to get it up to 30-40 mph in 1st then drop the hammer.
I drive it like a 2 speed most of the time in town 1st and 2nd (acts like 4.xx:1) and use 3rd like an overdrive. Obviously deeper gears and a higher stall would dramatically improve performance but it's fine for now even with it's 2800-4700 rpm power and 9:1 cr with a 750 single plane headers and something like 288/292 230/23? on 108 lsa .512" lift.
Works for me, maybe not for others.