The 300 was also called "Wildcat". The 2bbl low compression and the 4bbl high compression 300-V8 (310 Wildcat and 355 Wildcat.) Those goofballs at Buick never figured we would still be taken these things apart and putting them together 1/2 a century or more later, while dreaming up names over the water cooler. Here we are, driving Wildcats, running on Wildcats and being all confused... At least Duke isn't calling it a Nailhead.
65s and 66/67 have the heat riser on opposite sides, otherwise it should work. I saw a nice pair of 64s on the board yesterday, 64s have no heat riser.