[super_kit_car]

they should fit. what you need to check is the intake port height to make sure they match. I think the main difference in the GT motor, was the cam. I'm not sure if the 335 motor had a solid cam, but the 390 401 Hp motor had solids. In 67, the GT 390 was rated at 335 Hp. the stanard motor was around 275 Hp. If the heads are in good shape I would have them ported. you should be able to get 20-35 Hp for about $200-$400.