Anyone know of an M1D/M1C Cheek Pad reference guide in a GCA magazine? Curious if there ever was a good article on this subject. Know there were Vietnam era variants, but most reference only refer to the K-Line and 1950s MRT marked ones? I'm thinking there were 2-3 variants from the 1960-70s? Maybe some could also be called M21 Cheek Pads?