I took some pics of the 65 through 2/68 3 and 4 speed C5DA-A bellhousing.
Another site started a conversation on date codes which could be interesting here.
My 65 A-Code 2+2 has a clock style date code of 3/65 on a 5/18/65 door tag date car.
My GT350 also has a clock style date code with a 7/66 on a 3/2/67 Ford build date.
With a correct vin numbered trans I suspect the bell housing is original.
Here is a pic of MPC, casting date and cast number. The Shelby bellhousing could be a 6/66 if you don't count the little dot at 8 o'clock.