[Sirrotica]

There is 3 inches difference between a T 350, and a T 400 trans mount, or a 2 speed, ST300.

I've swapped T 400s into 65, 67, and 68 hardtops without any problems just using the standard crossmember, and drilling an extra hole on either side. I wouldn't spend the money for an aftermarket crossmember, but it's not my car, or my wallet.

Now if you have the fully boxed HD frame, or a convertible, you would need to do some fabrication to slide the tab welded to the inner channel rearward. GM first used the T 400 in 67, so they should have coresponding holes already.

I can't answer definitively about the gas pedal, but I doubt GM redesigned the sheetmetal of the firewall from 65, to 66. My best guess would be a minor change to adapt the later pedal, if there was any change at all.