dou is Waffen Wereke Bystrica in Czechoslovakia, BRNO's sister-plant. It is an East German refurb, what I call the late-pattern.
Early East-German reworks will often retain the original barrel, are force-matched and often have replacement beech handguarde, non-laminate. The safety is almost always electro-pencilled matching. they usually have semi-kriegsmodel stocks.
The late-pattern reworks are generally not force-matched (ie, left mis-matched) but refurbed to like new, usually with new barrel, but usually also with laminate handguards. They sometimes are stocked in refurbished wartime laminate stocks, and also sometimes post-war semi-kriegsmodel stocks.
Replacement stocks generally came from Czechoslovakia, as do the front sights. Both types had Czech sights, unless replaced after being surplused. It is suspected that the "east German Refurbs" were likely done under contract in Czechoslovakia, or that czechoslovakia provided the parts to East Germany.
The lesser-known "third type" are the tgf50 coded rifles made in small numbers in czachoslovakia in 1950 for East Germany. They were new production rifles in 1950.