identify this broken off boss that was jamming the clutch fork

SWAG:
Looks like it might be a locating hole for a dowel pin- check the engine to bellhousing mating area to see if it may have been forced together without being aligned, breaking that piece off the bellhousing...
It appears to be aluminum, so that narrows it down a bit.
A ruler or some object (a penny, for example) to give it some scale would be helpful too.