It comes down to large diameter vs. small diameter. The large flywheel/flexplates have 168 teeth on the early Stovebolts and late 250/292 engines and require the correct starter nose for engagement of tne bendix to spin it. The small fylwhweels with the 139 teeth for the Stovebolt and 153 teeth for the 250/292 take a different starter nose. Not sure how to look at the Stovebolt starters to tell what they fit since they all bolt to the bellhousing and I haven't paid that much attention to them, but the later block mounted starters have the straight across bolt pattern for the small 153 tooth flywheels and the staggered bolt pattern for the larger 168 tooth flywheels.
