At the risk of opening a can of worms, thought I would add my thoughts based on what Iíve read and what has worked for my set up. I have a mildly built 327 with a points distributor, stock coil and Crane adjustable vacuum can. Tools used were a vacuum gauge, timing tape, dwell meter/tach and a timing light.
I first wanted to determine the maximum total timing my engine would handle. With the vacuum advance disconnected and plugged, made a note of my initial timing and the RPMs where my maximum mechanical advance was reached. I would then make a full throttle run through 2nd gear and listen for pinging. If I heard none then advanced timing 2-3 degrees and tried again. When I heard pinging, retarded the timing by 2 degrees and did another trial run to verify no pinging. Made a note of my initial and maximum timing settings. In my case 40 degrees BTDC.
To set my initial, I first used the scroll plate supplied with the Crane adjustable canister to limit total vacuum advance to 7-10 degrees. Then with all vacuum hoses connected and air filter on, connected the vacuum gauge to full manifold vacuum. Adjusted timing to achieve highest vacuum attainable. Then retarded timing to drop highest vacuum reading by 2 inches. Compared my new initial setting (20 degrees) with my old initial setting and modified my mechanical advance so it would not exceed the maximum timing limit I had determined earlier. To eliminate any part throttle pinging, fine tuned the rate of vacuum advance using the directions supplied with the Crane adjustable vac can. So far no problems and car seems real responsive.