No matter how folks modify an engine and no matter what specs you think you need to follow, you simply can't fool a vacuum gauge.

Connect a vacuum gauge to manifold source and then prepare like you were going to use a timing light (vac. advance discon. and plugged). Advance distributor until you get highest vacuum and then back it off exactly 1" of mercury. This is on the money even if advertised specs differ. You also may have to adjust your fuel mixture and idle after this. Try it on a vehilce with known specs and you'll see it works.