Shoulder bolt? Can't ever remember seeing a shoulder bolt on a Mopar starter.
A stud in one retainer to the bellhousing and a bolt on the other? Yeah. Held in by random bolts out of my bolt bin? Yup. Never had an issue. Other than 7/16" bolts aren't as common anymore. So scrounging for one can be the hardest part of replacing a starter on one.
on the mini starters one hole is larger that the other but have same size mounting holes on tranny.. it needs a bushing to match or a shoulder bolt. Either works, they sell the bushings but i just made my own.