1966 mustang/new owner

Do you see anything like C6 which would be '66,or C5 which would be '65. Not uncommon for the block and heads to be different years. I was told back then they bought surplus and used them until they ran out. I think my original motor was a 65 block with 64 heads.

Tim and oneilthree, I think the letter in front of the numbers tell you the engine size. then the next two numbers are the equipment code that tell you things like which trans and water pump they put on. The R is for reverse rotation and the following number is the year (1965). The rest of the numbers are the serial #. The Interceptor code explaination I have is pre 65 but I will check it when I get home. I want to see what it says in the equipment code.

(GT21R526252) This looks like a engine ID number to me. I could be wrong but it does fit the info I have in my Interceptor manual.
oneilthree, The engine # should be stamped in the front engine cover above the tach (mechanical) drive housing. This is it.



Edit: If the number is off the front cover, then the first number 21 is the equipment code. Per the manual, it says that it has a Velvet drive 1:1 # 70, has a Sherwood water pump and Mallory ignition.

I also think the "G" is really a "C" that is cast in and not stamped in like the rest of the ID.