Actually, that site has a lot of misinformation and contradictions. The main GTO was actually a '68 Pontiac LeMans, a much cheaper car to buy than a very desirable '60s musclecar like a GTO. It then had GTO parts added to make it look like a '69 GTO. It had an auto trans, as is clearly shown in the movie, not a manual.
I still don't know the difference between a '68 and '69 GTO.
It made me mad that they wrecked these beautiful cars.