SoCal805, I agree with your recommendations... but if the distributor is set to provide 12°-14° initial "mechanical only" timing, you would shoot for an other 20°- 22° of mechanical advance in addition to the initial. The VA should not be considered when determining total mechanical advance. When the VA is connected, you could see a total of 46°- 48° of advance (mechanical + VA) during light throttle cruising... and that is fine.You want idle advance 20-24 (12 base +10-12 degrees of VA). Mechanical advance generally about another 12 degrees so that gets you to 35-36 at 2500-2700 rpm which is where SBC want to be
Dave, I understand your point and agree that the OP would probably be a lot better off with swamping out their non-VA distributor to a VA distributor... but unfortunately, the OP's MSD #85551 cannot accept the addition of a VA canister.OK, lets waste volumes of time and effort on "TESTS", instead of getting right down to it, and fixing it the right way in the first place. shall we.
The test doesn't cost anything (but some time) and is just a piece of mind for the OP before they consider spending $$$ on a new distributor with VA. The "test" is only duplicating how a properly set distributor (with VA) would preform at idle... and if there is enough of a rise in vacuum level to support the purchase of another distributor.