Here is a topic to chew on. I have always been told the 1964 race hemi engine package was an A864 engine package and the 1965 race hemi engine was an A990 engine package. Until recently I was pretty sure this was the case. Then I ran into a very knowledgeable in house connected person who told me they were all A990 in 1964 and 1965. Standing firmly on my previous thinking I told this gentleman the I have 1964 Dated blueprints of the "A864" race hemi engine and have been told by others that the 1964 engine was an A864 package. This person of in house knowledge told me he has heard the term A864 being thrown around but back in the day the talk was A990. He told me that even Tom Hoover referred to the 1964 engine as an A990, in 1964!
In my attempts to be as accurate as possible I always figured the different numbers made sense as there are differences between the 1964 and 1965 engines. Some of the differences are reported in many Chrysler documents. Here are some examples:
The 1964 race hemi had cast iron heads and aluminum crossram intake. The water pump housing was cast iron as was the thermostat housing. Alternator brackets were steel.
The 1965 race hemi had aluminum heads and magnesium intake. The water pump housing was aluminum as was the thermostat housing. Alternator brackets were aluminum.
Without going through all the details in print I can see these are two different engine packages. One thing for sure, Chrysler always had a different part number for anything with one change in it. A 3705 AFB max wedge carb is identical to a 3861 AFB race hemi carb with the exception of jetting. I am not trying to tick anyone off with this A864/A990 question but I would love to have people in the know weigh in on this.