My pre-WWII and later Marlin model 90's have the serial number stamped in 4 places. Under the receiver in front of the trigger guard; On the metal inside the forearm, (the forearm is held onto the barrel with a spring clip. Just grip the top of the forearm and pull hard.) On the side of the barrel assembly by the chambers (you may need to remove the barrels to see it.) and on the end of the butt plate (if the stock has not been cut off to install a recoil pad.)
Pre-WWII M90's have just numbers in the serial number. After WWII Marlin started using letter prefixes to designate the year made, for example Dxxxx. (1947) The gun was invented by Ole Horsrud ( his patent was assigned to Sears) and was produced by Marlin. It was originally marketed by Sears as the Ranger. Marlin introduced it as the Model 90 in 1937. One of my M90's has a 3-digit serial number, so it is possible that your gun has a serial number of 98. Check the other places on the gun to see if the numbers match.
Brophy, in his book, Marlin Firearms, A History of the Guns and the Company that Made Them, Stackpole Books, 1989, has an 8-page write-up on the Model 90. The book is out of print but you might be able top get a copy to read by inter-library loan. It also shows up for sale from time to time on EBAy.
Model90 12GA O/U
Moderators: Regnier (gunrunner), JohnK, Sure-Shot
Re: Model90 12GA O/U
BarkeyVA
Re: Model90 12GA O/U
Now I'm confused! My previous post was supposed to be a reply to someone who just inherited a M90 and asked if the number 98 on the bottom of the gun could be the serial number. I don't know what happened to the guy's original post! Is this a sign of old age??
BarkeyVA