The Yougo M53 has a few differences with the MG 42. I can tell yours is an M 53 because there is no mount on top of the bbl jacket for the AA sight.
Since the M 53s were built after the Korean War - 1953 - 56 approx - I don't know what you are referring to with the 1943 & 1937?
Bbl change on an MG 42 or M 53 was 12 seconds for an experienced gun crew.
Sarge
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