I believe that all '50s and '60s Chevy starters had the same 9 pinion teeth. From the start of 12v in '55 through '62, ALL Chevy flywheels were 168T. I don't know how far back 139T/6V went. In 1963, Chevrolet started using 153T for BBCs to spin the engines a bit faster, although not all BBCs got the 153T flywheel. The difference is in the bellhousing casting, until you get to the "bolt to the block" starters.
Best wishes,
Les
