i have the same problem its a 68 f100 with a grannyed out 4 speed but i got a 9" with 3.70 gears and it used to be a colum banger 3 speed. i have a 360 in mine to with a holley 4 bbr tops out at about 90 or so but its not the top end that wins its the quickness, but i think i'm going to but a c-6 in mine it should be quicker