I just picked up a 35 rem.,Marlin 336.Unlike most Marlins that I have seen,it has only 336 stamped on the bbl and no letters like c,cs a,etc. Does that have something to do with the time that it was made?
There was a period where Marlin called them 336 without any other letter designation. The various letters usually indicated a modification in the rifle. If you look at the reference section there is a listing to look up the dates of manufacture on various Marlin rifles.
It went from Model 1936 to Model 36 to Model 336C, 336A and 336SC the C stood for Carbine the A stood for rifle and the SC for Sporting Carbine. All three were made at the same time starting in 1948 the C was made to 1983 the A was made to 1962 and the SC until 1963 There was also a 336A Deluxe rifle during that period. In 1970 there was a 336 100th Anniversity Commemorative, and a 336 Zane Grey Century. 1973-80 There was a second issue 336A and in 1973 a 336 Octagon. Lots more info on these in the Marlin Firearms book, A History of the Guns and the Company that made them by Lt. Col William S. Brophy (best book on Marlins that I know of).