If the bolt serial doesn't match make sure to get it headspaced before your shoot it. It's generally not a big issue with some milsurps because bolts were replaced by armorers, but at the beginning of the Spanish Civil War the Republican government essentially armed the leftist militias by opening up the armouries. Bolts had been stored separately from rifles and they got mixed and matched by crowns passing around rifles and boxes of bolts with no regard for matching them or checking function. Mine fits really badly.
I've seen enough Spanish Mausers with stocks finished similarly to yours that I think that's probably an arsenal job, though it is quite different from the factory finish. No evidence to base that on, just an observation from years of collecting and being interested in Spanish guns.