Aside from all the other odd aspects, the head badge decal looks fake. I'd put some money on the bike being a non-US-made knockoff.

Edit: after another look, the head badge appears to be painted on, and with obvious orange peel from a bad paint job.

If the components work reasonably well and the bike isn't otherwise damaged, it's probably worth replacing parts as needed to keep it running. But given that it appears to be a fake GT, I wouldn't bother trying to restore it to resemble a genuine US-made GT.