Hello: I am in the market for a date correct 1966 273 motor. I have found a couple early casting date motors, August and September 1965 that have heads that have casting numbers 2465315. That number is for a 1965 motor. Did Chrysler put 1965 casting code heads on some early 1966 motors? I thought that the 1965 heads were not interchangeable with 1966 motors. I would appreciate any help on this. Thank you. Bob

 

Any Mopar is likely to have previous year casting numbers. You have to remember that year models back then were introduced in the fall of the year previous to the model year. "It took time" to build and stock parts for assembly.

I don't remember the actual angle difference, but you could determine the early / late heads by measuring the intake bolt angle and comparing to a later head. If you have a known set of late heads or intake, you could easily physically compare them