This is a cutaway display model of Optimus No. 7 with burner 207 from the 1930's. The number on the tank is in the cut-out section, but I am assuming it's the same as the No. 7 presented in this catalogue: https://classiccampstoves.com/threads/1934-catalogue-no-1260.31160/ These cutaway displays are excellent for showing the design and function of stoves. This one has an early generation 207 burner where the cleaning needle is in the upper position when the burner valve is closed. Other time markers include: tank bottom and side embossing indicate "Stockholm" instead of "Upplands Väsby", air screw is marked Stockholm, dimpled spirit cup and old style cookie cutter with tactile lettering.