Some authoritative information suggests that Marlin Models 336 were first D&T for top mount scopes in 1956. I pass this on with no solid information to contradict it. Certainly it was no later than this date, but possibly earlier. I know that my several rifles made in 1953 are non-tapped. I believe that if the older striated receiver top design is present (versus the smooth sandblasted top), there should be no original D&T present.
In any case, sometimes even a careful inspection can lead to false conclusions. Normally it is easy to spot non-original mount holes, but occasionally a quality aftermarket job may be indistinguishable from factory production work. Also, if the rifle has been refinished, the screw blanks will often match well enough to suggest D&T originality (regardless of whether the reblue appears original).
My take.
Last edited by iskra; 10/27/11.
