What to do to get a quicker launch...

I think your centrifugal advance is coming in way too quick, if it's really all in by 1800 RPM as you say. Should go to about 36* around 2500 RPM or so. Also, as far as vacuum advance goes the more the better. Just keep dialing in more and more until there's pinging going up slight hills or when accelerating slowly. 50*+ a few is about right for final + vacuum advance.

I think the best course of action would be to pull your 904 and rebuild it with the A-999 gearset (lower 1st and 2nd gear), a good shift kit, and a good 2600 RPM stall converter. That might work out nicely with your stock gears (which are 2.94's, right?) but you'll "round out" the drivetrain with some 3.23s or 3.55s. I think 4.10s are unnecessary and will make highway driving a nightmare. They may make your launch very quick but top speed, gas mileage, and engine longevity will become issues with your mild 318.