Is your's one of the Great American Game Series rifles? Brass medalion in the stock,,ect.
The last round hold open was officially intro'd in 1985 in the 22 autos, but I've seen it earlier than that.
The American Game Series rifles were made from about 83 to 89. Each year placed a different animal in the brass disc into the stock.
Made on the M75Marlin, which was an upgrade of the Glenfield M75 which didn't exist anymore 'cause they discontinued the Glenfield marketing name (83).
It's all the same action anyway. M60, 99, 75, 989,,,
The series was made for a Hardware Store chain, but who I cannot recall.
If they still run the serial numbers on the M60 series receivers the way they used to,,add the last 2 digits to '68' and get the year of mfg of the receiver,,and usually of the rifle. Maybe they've changed that since they started #'ing them in '68.
We destroyed an awfull lot of return for repair waranteed rifles that were pre-68 unser#'d. The whole rifle. Model 80's too.
Hope this helps.