Hmmm....3.55s or ???

My 70 ran a best of 15.3 when it had:

stock 318, with a 340 singleplane intake and a 600 CFM Holley (dual points dist.)

727 with a stock converter

2.76 open rear gears

This is a full weight car also (well, not now as it's missing it fenders), I would think you could get better with a 4 speed, maybe something else is up.