What was the year that Marlin began drilling the receivers for scope mounts?

I'd sure it was prior to 1952. How 'bout 1949?
TR

So it is possible that a 1957 336 would be factory tapped?

My 1953 336SC is not deilled and tapped. It has a plain flat top reciever.

The receivers were drilled and tapped for scopes in 1954 for centerfire 336, and in 1956 for the .22 model 39a's.
Hope this helps.