What Year Did Cover Change?

There's four distinctly different designed LA covers that I can think of off the top of my head:
Early LA up to '68, which used a timing tab that was attached by the2 bottom water pump bolts.
Late '68 and '69, which had a cast-in timing tab on the passenger side.
In '70 they switched to driver's side timing marks to accommodate the new aluminum water pump with a passenger side inlet.
As previously stated, they later ('80s? or somewhere around there) revised it to allow changing the seal from the outside.
Technically, any of them would physically fit your motor, but only the ones up through '69 have the timing marks on the passenger side.