What is the part number of your point-type distributor? 1951 was the last year for distributors with anywhere from 33-39 crankshaft degrees of centrifugal advance, depending on the distributor part number, plus another 10 or so from the vacuum advance at light-throttle cruise.
In 52, the centrifugal advance dropped to 16 1/2 to 19 1/2 depending on part number plus another 9-11 from the vacuum unit.
If your HEI is getting 20 crankshaft degrees of centrifugal plus 10 or more vacuum advance, I'd leave it as is, or use a delay-flash timing light to set the max centrifugal to about 25 crankshaft degrees or so at 2500 RPM. The vacuum should add 10-12 degrees to that at light throttle cruise for better gas mileage.
Several years of dyno testing of a lot of different engines has shown me that one degree of over-advance robs as much power as 5 degrees of retard from the optimum setting at full throttle, so it's best to err on the side of "not enough advance".
Jerry
