Re: Another model 90 question
According to Brophy in his book on Marlin Firearms it was around 1950. As I mentioned in a previous post, I have a "G" serial number 12 ga. Model 90 made in 1950 that is open between the barrels. I have a "D" serial number 16 ga. made in 1947 that has the rib. However, there must have been a transition period because I also have a "D" serial number 12 ga made in 1947 without a rib between the barrels. The best reference book on Model 90's is "Marlin Firearms, A History of the Guns and the Company that Made Them" by Brophy published in 1989 by Stackpole Books. It is out of print but I bought my copy on eBay. Do an internet search and you will find it listed by other internet book sellers. I initially got a copy to read through inter-library loan at our local library. Brophy devoted 8 pages to the Model 90, and on page 629 is a list of date codes.
Introduced in 1937, there are no serial number records for Model 90's made prior to WWII. After WWII Marlin started using a letter prefix in the serial number to indicate the year made. For example, D-1947, E-1948, F-1949, G-1950, etc. Marlin did not use an I, O or Q in the serial numbers. Very early Model 90's may have had an oval with ducks "engraved" on the frame. Around 1939 to 1941 some Model 90's came with a bird dog scene on the frame.