Having Problems with engine ID clarifiaction (273 photos)

Hi All,
I'm once again terribly confused and need your Mopar Jedi Wisdom. According to my Vin I have a 1966 Barracuda 273 2bbl. The engine casting number is 2465330. The stamp on the driver's side block below the head is B 273 10-29. So far, so good....but....My Pistons have 4 valve reliefs. My Manifold intake bolts are 9/16 but My driver's side cylinder head is 2465315(1964-65). From what little I have been able to find, none of this adds up.

Here is what I have read:

4 valve relief pistons=1964-65 2 barrel 273's.
2465315 cylinder head is 1964-65 and their intake manifold bolts are 1/2".

Any input to help me solve this mystery? Only guess I have is that someone took earlier heads and pistons and put them on a 66 block. Still doesn't solve the intake bolts though........