Vacuum advance issue

I have a 1970 Duster 340 that needs 100 octane gas (stock). In order to make it run on 91 octane (California), I disabled the MECHANICAL advance and run initial at around 10 degrees, and then tailor the vacuum advance to yield the most advance without pinging. I outran a 1969 Hemi Road Runner with this car, so does it work? Ohhh you betcha!