The OEM cover is long gone due to a hole into the oil.
The one on now is a 70 up
The other 2 covers are both 65 castings, I did not note their part numbers both have the hole
My block is a 2806030 I don't know when it was cast but it was assembled 12/66, and another 68 318 block I had (photos) was a 2536030. Neither have the hole.