You may have answered your own question about the advance. Better at 22º than 12º, so why not try it by the seat of the pants and slowly bump it up from 12º and see what's best? Don't forget that when you hit the pedal your vac advance all but disappears.
For your rich/lean fuel try checking to see that you have NO gasket leaks anywhere in the intake system.
Is there a particular reason you used 305 heads? Are the valve sizes the same? Any idea what the chambers measure in c.c's?