well, it has no 990 mounts so that puts it later than 88 or 89.

and it has a coaster brake tab.

the original GT Performer came out in '84 and the same thing.
the year on that frame is 86-67.

what type of riding are you going to be doing on it?
street? the dropouts are too thin to hold up to any of todays abuse.
flat? the head tube angles on those things are shallow, good luck. (unless your doing old school stuff, then have fun)

you might want to NOT paint it, as the value of the frame will be higher in original colors.
there is a HUGE resurgence(sp?) of old school riders building up their fav. bike from "back in the day"

if you REALLY want to know the year go to www.vintagebmx.com and ask there.