**** Dawg---The early (Very first) Mini's had serial numbers completely different than what we normally see. Like cajungeo says a call to the factory will confirm the date your Mini was built. I would be real interested to know if it has a roller engagemnt on the bolt or the regular little nub that engages the operating rod. Anyway a call to Ruger will give you whatever info you want.
Good shooting
Bushwack