If the bolt shroud is original to the action, the serial number is also engraved on one of the bottom flats of the shroud.
I recently rehabed a 1375. After quite a bit of work on the cocking cam, shroud and cocking piece helix on the bolt body...it shoots very well. If you do that work, you can lighten up the original spring tension quite a bit. The firing pin travel is stopped by the the front of the cocking piece hitting the front of the cutout in the bolt shroud...so keep that in mind if you start doing any work.
Good shootin' -Al
