Welcome to the forum, Janne.
Your pistol is interesting, in part due to its strangeness and aspects that would seem to contradict themselves--or at least what one would generally expect to see.
This is indeed a "long frame" gun, and the barrel is, of course, not original to its extension. The "GL" monogram on the rear toggle link was ordinarily applied to prototypes associated with Georg Luger's involvement. The toggle links are definitely the old school arrangement. The breech block sports a hole on the bottom to allow for gas venting in the event of as pierced primer, which is a "Scandinavian feature". If the barrel extension has been shortened to fit the barrel, it is a shame. The use of a coiled recoil spring instead of a leaf spring is notable. The bell crank in the frame needs to be of the type to specifically accommodate a coil spring and its guide, and the frame and upper combo are compatible in this way, despite their serialization's single digit difference. There is, however, a blue "heat stain" on the frame in the area in which this arrangement would be found, and a matching burn mark on the corresponding area on the back of the right grip. This would indicate that some welding has been going on, perhaps to adapt an old model frame to a coil spring recoil system. The replacement barrel's flange has also been messed with, because there's not much of it remaining. The "B" suffix would seem to relate it to this variation (
https://phoenixinvestmentarms.com/2146ProtoFBGL02.html)
Let's see what others may add as observations or explanations about this pistol. The GL monogram, if original, is certainly intriguing.