THe rules are somewhat confusing.
However, regarding grandfathering, it's pretty simple. In order for it to be grandfathered, it had to be LEGALLY in ASSAULT WEAPON configuration when the law passed.
So, if you had an AR with no flash hider, no thread for such, no bayonet lug, and jsut a psitol grip as a banned feature, you're screwed. It is un-grandfatherable.
One portion of the AW bill to remember; it also outlawed several firearms by name. one such banned name was Colt AR-15. So, if your rifle was stamped Colt AR-15, it is legally a pre-ban AW.
As for the MAK-90, it appears as if the folding stock was put on illegally. THerefore, when the bill passed in 94, it was illegally in AW configuration. So, i would guess that would make it legally a post ban, and the folking stock should be removed ASAP.
I'm no lawyer, and i don't pretend to be one. But i have looked pretty deeply into the topic, and i did stay in a motel 6 the other night.