Sorry, heers68, but I have nothing to add, except, perhaps, your Wilke gun was certainly made and proofed in Suhl, not Zella - Mehlis, as the word NITRO is in block letters, not script. So it may have been made up by anyone in Suhl. Raimey ellenbr already told you about the possibilities. The problem is: No German gunmaker ever said: "Sorry, we don't offer such a thing." If a customer asked for a special gun, he would say:"Of course we will build that gun for you." Then he would farm out work and buy in parts or even the complete gun, even from his competitor next door, and sign it as his own product. Well the EK stamp looks like a barrelmaker, so it may be one of the Kelber dynasty.
It is impossible to pinpoint a model or maker from such details as a horn trigger guard or caartridge magzine in the buttstock, as these were essentially special order additions that could be added or left off at the whim of the customer.