The easiest way to tell the difference between a 66 and 67 is, the 67 had a chrome mesh grille vs black plastic, the fender GTO emblem is mid fender on the 66 and low on the 67, the tail lights are split on the 67. There are more, of course. The 67 used the 400 and TH400. Great cars!
Pontiac was using the Super Turbine 300 2 speed like Oldsmobile before the TH400 right? It's interesting that Cadillac & Buick had access to the TH400(ST400) in '64, And Chevrolet in '65 but only behind the new Mark IV 396.