Please correct me if I'm wrong, but you are suppose to tune (jet) to achieve 11-ish AFR at WOT. Then from there your can adjust your idle screws lean at idle. Also if your cruise is lean, so you are going from super lean to rich at boost, try putting a vent tube extension in. It will raise your cruise AFR. I am using a 8" one that richens up my cruise just right.
I am also running a HEI. I installed a lightweight advance kit from summit and after many combination's, the lightest springs worked the best. It allowed my rpm advance curve to ramp up quickly and max out about 20-25 degrees advance. (all-in) >> at idle 11 deg and by 1800-2000 rpm im at 25 deg. This is an estimate, I have no TACH. All measured with a dial back timing light.
