760 Gamemaster date quandary

[Marbles 427]

Hi all,
I recently acquired a nice condition Model 760 Gamemaster in .35 Remington.
It has a barrel date code of EYY which I think translates to Oct 1952.
It has the metal ejection port cover.
It has the 5 Diamond forend and checkered grip with grip cap.
Factory sling mounts are present.
It also looks to have been factory d/t with filler screws present.
My question is regarding the 5 Diamond checkering and d/t holes.
From what I can see these options weren't available in 1952.
Is there any evidence of 1952 model years having these features?
Thanks in advance.

[Marbles 427]

After further research I have determined that the receiver serial number dates to around 1957.
The fellow I received it from says it came that way.
Could this rifle have come from the factory in 1957 with a 1952 barrel and metal ejection port cover?

[Marbles 427]

Is there any way to determine whether the rifle has been remarried?