From what little knowledge I've gained over the past few years, that looks like a 65. Is it a real GS??

We would need someone to go over this one in person to find the GS specific items. The VIN would also reveal the year, unless it's been altered. It's also possible that the seller made a simple typo, and never caught it prior to posting the ad.
Note that the ad says "350 Chevy crate engine", so what became of the GS engine mounts??

I'm not ready to call

on this one just yet.
