318 or 273??

Hi everyone!! I just bought a 66 Valiant 2 door with a V8 last week and the guy told me he pulled the motor...a 318...from a 66 barracuda.
However, this motor has factory adjustable rocker arms on it, which I thought only came on the 273's in and around that year. It's not a 318 poly, it's an LA style engine...I do know that much.
Judging by the amount of crud, sludge, flakes, and build up I can safely say that they belong to this engine and haven't been pulled from another.
I know the casting numbers are on the side of the engine block but I can't get to them to see the the size and year.
The head casting numbers start with a 2 and end with 5315. I can't read the 2nd and 3rd number.
Has a Carter 2 barrel carb.
Any help would be appreciated.

Did they even put a 318 in a 66 cuda?