Buy the rifle for $750 or less, drop in a 7.62 Nato no-gauge (not 308) into the chamber and try to close the bolt.  If the chamber doesn't eat the gauge (read bolt won't lock closed), your dam near golden.

The only thing that I would sugest is pick up a USGI spring set (less than $30) and re-spring the whole rifle.  The stock imported springs may be fine, but they are questionable in regards to longivity, and the recoil spring may be on the way out if the rifle has been fired something like over 4k rounds.

P.S. baring some comsmetises ( different production dates), the poly's and norinco's are one and the same.

P.S. if you can find either brand of these rifles for under $700 as a common. IM me and hook me up on a deal!!!!