What classes in the GNCC can a 1987 polaris cyclone 250 2-stroke race in? If not the GNCC than what other type of racing could it run?

Probably the stock class, or utility class. Those quads are definately out-dated, and were never meant to see any type of racing. But, however, if he is up to the extreme challenge, I say go for it. It will be way tougher on him, than on the other riders, but you don't even have to finish if you don't want to. Remember, the first few races is about learning, and getting in shape. Take it slow, and at YOUR pace. Good Luck.