Thunder Tigre did at one time make C/L venturis and NVA's for their engines. The venturis were a little on the large side for the displacements but the needle valves were fine. They were apparently dropped for lack of sales.
That front hole puts the needle valve uncomfortably close to the spinning prop. Thats one engine where a rear mounted assembly and fuel nipple would be fine and the one from the OS LA 25 will fit fine. Any of the after market suppliers including the forum host can help you with a proper venturi, Cost is reasonable on the Venturi and you can probably pick up the rear mounted NVA from someone who has converted their OS or as a last resort get one from Tower Hobbies.
Others I'm sure will have more help for you.

Dennis