Flywheel Question - HELP! - Big Block vs Small Block???

I'm looking to buy an externally balanced flywheel and have found some are advertised for small block AND big block wheras some are big block or small block ONLY (same tooth count).

I'm looking at a 130 tooth wheel and I see them listed for both. What's the difference?? Is it the bolt pattern for the crank?

Thanks

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.