[MCKUltra]

Bought a 61 Bonneville, CA built car. Was told it was likely 389, thought it was a 389 until I looked at it.

538181 Block and has the 421 transfer lug, 538177 Heads. Had to PB/brush a lot of crap off the date code, best I can tell with a borescope it's C 28 8 (look like 8's which would be incorrect) or C 2 3/8 3. No visible stamp on the metal under the passenger side head even after using acid to clean/etch. I may have to pull the timing cover to find something? I do not see a chamfer at the top of the cylinder with the scope. I still have to scope to see if it's 4 bolt.

Thoughts on the date code and no markings on the front pad?
I'll upload photos from the scope once I find the card for it.