I believe it was a 'AA' in the '64, because I bought a 'AA' over the counter for the engine I built several years later ('68) to go in my '67 Cougar XR7 GT.
The Cougar came, of course, with a 390, but it never was satisfactory, so I gathered a bunch of parts and put a 427 together for it. The pistons I found were a set of the C8AX pop-ups, so I had a bit of trouble even with 260 Sunoco, and put a home-made 'Snow' type set-up on it that ran isopropyl alcohol to cool things off. I used an adjustable Hobbs switch to trigger it and found that it removed the tendency to 'crackle' under low-speed load.
The 'AA' cam, with shell lifters, was relatively mild for daily driving. I used an 850 DP carb that I had gone through by Harold Droste, the Holley guy that worked all say, every day, at EEE. The carb was mounted on an early, modified Sidewinder. That carb was designed to use of the 427 Cobra, but Harold worked his magic and it functioned vety well.
I went through the C6 that came in the '67 Cougar and used an aftermarket converter. Headers were intended for a 390 Mustang, but I cut the flanges off and substituted a set of 8-bolt up-'n'-downs. The gaskets weren't known for lasting well. but I got good at unbolting the motor-mount on one side at a time for room to get my hands in the vivinity, and whacked-up a few box wrenches to fit. Using gaskets made up of two layers of gasket material with a perforated steel core also helped.
The street characteristics of the two engines were close enough that I'm sure they were both 306 instead of 324. FWIW, I asked Comp for a solid roller that duplicated the street manners of the 'AA' when I spec'd the parts of the engine I built at the Roush prototype shop for Mustang Illustrated. What they gave me was 242-248 at .050, and about .666 lift on 110, but the idle characteristics, on the dyno, were just fine. a bit of lope at about 850 let one know, along with the mechanical sounds of the lifters, was all quite glorious. We've learned a lot about cams since the '60s.
I might also comment that we used a C8AX-D in the Thunderbolt/TP combo I helped with in '68. Much rowdier.
KS