The heavier barrel, the sights and sight guards, the feeding assembly in the magazine [with pressed *dimples* to better guide the rimmed cartridges and prevent rim hangups during feeding] and the sling swivels, suitable with a wider sling that spreads the weight of the rifle over a wider area of the shoulder preventing fatigue during long marches- or skiing- with a slung rifle.
Yeah, after I posted that I did some research. It seems that the 1939 version got all the improvements that were made to the rifle over the years.