Yes, it will fit.
The spring mounts are different on '67-up but I think the 65 springs will still fit.
64-66 had a flat spring pad and used a bolt and retainer plate to secure it to rear.
67-up had no retainer plate but the mount had a raised center which the spring sat around. Spring mount in frame is different too but is irrelevant here.
GTO rear may be an inch wider, you have to measure to be certain.
The GS used larger wheel bearings, and in 1966, larger diameter axles. Unsure what GTO used.