I'm converting my 65 Barracuda to a 4 speed also. I'm going to hold off welding my 4 speed hump in until I get the transmission mocked up. My hump is a 64-65, just like yours. I might be overthinking it, but I'm guessing with that itty bitty hole for the shifter handle....the hump placement may need to be pretty precise. 66 model humps had an elongated hole for the shifter, like later A bodies.