It was imported by Dominion Investment Group through Virginia making it a 90's imported rifle after the 1994 Assault Weapons Ban. it is either an SA93, SLR95 or SLR96. Without seeing a picture I can't tell you which one it is but look those up here on the web and you will likely find some information. They all came into the U.S. with thumb hole stocks for compliance but might not have the original stock, etc. Sounds like yours have been changed. It is probably an SLR95 those were most common.

Either way you are probably holding one of the best AK variants ever imported into this country. Before things got heavily rolling for the "civillian market". Of the three the SA93 is possibly the "best" it was a Bulgarian Type 3 AKK only semi-auto. It was the real deal effectively identical.