456 gears

I'm going to say timing and jets.

Go to a test and tune night at you local drag strip and start tuning for maximum trap speed...forget the ET for now. Make a baseline pass, then bump the timing up to 34° and make a pass. If it picks up a big chunk then try 36 (I bet it will like 34-38°). Next jet it up 2 sizes until you MPH drops, then back up one size and you should have the jetting dialed. After that, then start messing with launch rpm and begin to get a handle on that 60' time...one step at a time, but get the motor making the power first before you start worrying about ET.

FWIW, last fall my old motor picked up half a second and 6 MPH when I took it from my high altitude nitrous tune (28° timing) to low altitude All motor tune (35° timing and jetted up 4 sizes).