Robert,
The starters are not all the same. The early bell housings had a smaller starter hole and the starter bolted to the bell housing through a end flange. The later starters have larger end bell and a larger hole in the bell housing and mount via long mounting bolts that go into the block. Just match the starter to your bell housing and match the tooth counts (I checked my tooth count and it's 168).
My Fire truck has a 13" clutch (322 Buick motor) and I run an 11" in my tow truck with a 350 SBC. If available I think 12" would be perfect.
Mike B
