External balance will be engine specific. Neutral will be by tooth count only. The BB and SB are 6-bolt flange and are identical. In 70 or 71 they went to a scalloped clutch...10.95" disc and hat that bolted to a 10.5" flywheel pattern, so then the BB and SB could use the same flywheels...aside from the aforementioned external balance issues that were specific from engine to engine.