[Rev]

The 351 is taller and wider. It will fit the '65-66 with no shock tower mods. Hooker makes dedicated headers just for that swap. You may need a drop drop down air filter for hood clearance. I haven't done that swap, but Ive heard it's really easy. The 3 speed may or may not hold up with the extra torque, depending on how much you abuse it. You probably will want a top loader 4 speed and a better clutch anyway down the road.

Rev