One trick that works well is to run between 18 and 22 degrees initial but then use a relatively slow curve that gives you full advance around 2800-3000, too light a spring gives you full advance at the crack of the throttle, they do that primarily for heaviier underpowered cars to give them some extra "oomph". With a 512 that is not a problem, if it's set up right and the combo is HAPPY, it should feel like a really strong horse that you need to pull back the reigns on most of the time.

You can run zero deck closed chamber with an excellent quench pad and still run 11.4-12:1 in a 512, in fact I recommend it....but that would be a dished piston. A flat top will be over 13 at 512 with any typically sized 75 cc chamber.