64 and 65 heads should be #315 or #178. Now I say "should be". All the books and lists I have seen say the 920's came out in 66. Was there a production change in 65 for the 66 model year and some 920's were drilled for the 65 intakes to finish the 65 production year out? Could be. The head numbers are just a casting number and can easily be drilled for different year designs.