If you have access to a delay-flash timing light, try setting the timing to 35-36 degrees at 2500 RPM with the vacuum advance disconnected. That should put the initial advance at startup somewhere in the 10-12 degree range. You'll get another 10 degrees or so from the vacuum advance for light-throttle cruise and improved gas mileage. I've done a few hundred dynamometer runs on Chevy 350's, and almost every one got its best full-throttle power with centrifugal advance in the low to mid 30 degree range, regardless of camshaft or compression ratio. The only reason not to run that amount of high speed advance would be if it's difficult to crank the engine due to too-early spark timing.
Jerry
