I just picked up a marlin 336 in 30-30. The receiver has been drilled and tapped for a scope base mount. My question to anyone who might know " is the receiver drilled and tapped at the factory or is this an after market job" . The screws that are in the receiver now are way to long and stick up from receiver almost 1/2 of an inch. I plan on trading this gun for a shotgun and the guy who wants it does not plan to use a scope so he wants the original or smaller screws. I was wondering if I could order new screws from the factory, or if it was an after market job I will have to find someone to measure the diameter and twist etc. Thanks for any info.

depends on how old it is , all of the 336' s that i know of have been drilled and tapped for a scope at the factory but , like i said it depends on the age of it , to determine that you should try to contact the maker ( marlin ) and give them the serial number and they should be able to tell you . what is the exact model designation buddy ? 336 cs , 336 sc , 336 t , you should be able to get screws to replace them from the marlin factory but , try your local gun smith first , i' m sure he' d have some .

The serial # is 19120719. But the data stamp only says 336. How do I know if it is a CT or whatever?

it would usually say on the barrel , right after the model number like on mine for example , " model 336 cs " , so yours is probably an older one , you should give marlin a call . or you could take it to take it to a gunsmith and have him see what size holes they are , and what he has to fill them

P.S. - i think you should edit your post to take your rifles serial number out of it , that' s not something that you want to divuldge

Good advice Whelen on all accounts.S/N' s are a private matter and shouldn' t be viewed by the general public. That' s what they " X' s " for. Eg 123xxx.
Ruger Redhawk

Try savage99.com
I have found lots of info on dates of manufacture for savage,winchester and marlin.
Good luck

Just call up Marlin and ask them about it. They have pretty good customer service.