Hi Matt.....welcome to TFF!
For military firearms, "mix-and-match" parts are not the exception, they're the rule.
During their history, most military firearms, were repaired, rearsenalled, had various parts replaced when they were broknen or worn out.....in addition, they were often used on a gun range, after which a whole bunch of them were broken down and cleaned, and put back together in no particular order.
Soooo.....don't fret, the M37 is a great gun, and you've got a nice piece of WWII history.
Here's a bit of info on the M37: