A couple of things at work here. As another said, if you're into "classics", fine, but the '68 is nowhere NEAR the performance potential of the late GTO.
There is no such thing as a "Hurst 4-speed". The shifter was made by Hurst, and if the bar comning through the floor is round (as opposed to flat), it's original from Pontiac. The transmission is a Muncie (only 4-speed Pontiac used during that era).
A 350 car won't demand the value a 400 car will, either. While not a bad performer, the 350 Pontiac is no match for a 350 Chevy OR a 400 Pontiac.
That's all...
Jim