The advance is probably 10 distributor degrees, which translates to 20 degrees at the crankshaft. No problem there. I like to modify the centrifugal advance (not vacuum) curve to reduce the advance by 8 to 10 crankshaft degrees, and add that much to the initial timing. It makes for better acceleration, particularly with an increased-compression engine like a 250 with 307 V-8 pistons. I takes a distributor tester to do it right, though. Use whatever plug was reccomended for the head you're using, and gap them to 40 or 45 thousandths.
Jerry
