Trans date matches the POP P0522

Right! 2L for wide ratio, not W!! Thanks for correcting me on that!

Nice to see there's a POP existing. That helps to confirm things.

Is the dealer page readable? I'm curious what dealer it was sold from?

Also, get the casting number from the Muncie case. Body was built 4th week of March and trans was built almost 2 months after that? May 22nd. I wonder if they used a leftover 65 M21. It's probably 3851325. I'd be surprised if it was 3885010, as the POP looks ok but a pic of the dealer page would be helpful.

Isn't the 12 bolt rear dated September 17?

And it's a Sweetheart Engine - Valentine's Day stamping...

So, is the original distributor there (1111074), air cleaner?

Yes 9/17/66. I've seen that date several other times, used as late as on a May car! Low volume axle, which makes sense.

Should it not be dated 9/17/65 instead for a '66 model?

right! Typo on my part. Would be interesting if muncie was a 3851325. maybe part number tag is still attached to sidecover bolt

Yes 3851325 on the Muncie