Since a mini-14 didn't usually come with a flash suppressor or pistol grip, most of them, unless modified by their owners prior to the ban, do not qualify as grandfathered, pre-ban rifles.
A Mini-14 would have to have been configured with at least two "evil features" on or before 9/13/94 in order to have been grandfathered. If it was never built into a "saw" configuration before that time, it's not considered a grandfathered semi assault weapon under the letter of the law.
Now, if it's been sitting in your gunsafe since the 70's, there's no way the ATF can prove you never put a pistol grip and flash hider on it, for a lark, in November of '82, then switched it back without telling anyone - which would legally make it a grandfathered "saw".
Crazy laws make for crazy fun!