All Polytechs were "preban" as the last one was imported before the original ban went into effect. That means that the "evil bits" are ok on the beast.
I'd suggest that you check "Different's" long essay here:
http://www.imageseek.com/m1a/welcome.html
His work will confrim that your rifle is a preban because of the date of manufacture.
Now, all that being said, make sure you check the headspace on that rifle. If you don't have gauges, I'd suggest that you load one round (surplus NATO rounds only) and secure the rifle as you fire it down range. Then inspect the brass. If the primer looks ok and there are no brass deformation, you should be good to go. Remember, only surplus ammo unless you have he headspace checked. Commercial ammo has a different thickness brass and softer primers.
I've got a set of gauges which I lend out to fellow shooters but right now they are on their way to Kalifornistan. When they return, I'd be happy to lend them to you if you email me directly with name and address. I'll send you the go, no-go, and field reject gauges to check your bolt/receiver.
Rome