The only difference I know is the 65 block has no oil groove in the back cam journal. The 65 cam has a groove all around the back journal. The 66 doesn't. The 961 was the 2-bolt and the 962 was the 4-bolt for both 65 & 66. The chevelle vette and Imp all used the same intake the 963. The carbs were the same cfm, just diff. #s. The heads 208 & 858s same valves 2.19/1.72 and same size combustion chambers 108.989.
Piston weight was diff 24.00 oz. to the 66 piston 23.13 oz.
I don't know of any differance between them.
That's my story and I am going to stick with it!!!
