Rem Model 12 help, Year & Parts

[FCSpringer]

Hello. New to the site. I have been on google for a couple days and dead ends. I found some chat here on the model 12, and a fella by the name John Gyde keeps popping up. So I hope you or someone else smarter than me chimes in LOL. Thanks in advance. First it is a 24" octagon barrel, a 12C it seems. 1st ? is, what year with a SN 578472 ?

2nd ?, is there a place to find a plug and play firing pin that does not need to be all ground to fit? This one is broke.

3rd? The serial # is not the same as the one on the trigger group, is that normal? or is this a piece together from a couple guns?

Thanks for any help I can get. I would just like to get her back in working order. It was my grandads gun.

[admin]

1922 - should be date code stamped.
https://www.remingtonsociety.org/manufacture-dates/