Interesting puzzle, Sadly, not a Falke 90 unless there is a variation in fore ends that I do not know about. More likely an Original (Diana, Gecado) 50 variant. I'm afraid that Originals are not my field however I recall seeing photograph on the BBS of a model 50 with an extended forend. I can see the similarity with the Falke where the stock joins the receiver, the lines are very similar. Well spotted and good luck in your search. Doubtless Galvin will put you right shortly.
MarcDV.