Thermal Hopper through firewall

I would appreciate advice on installing a Cox Thermal Hopper .049 engine through the firewall without a cage mount. It is for a Goldberg “Blazer”. I have made a 5/8” diameter hole in the firewall as per the engine instructions, and will have the needle valve and fuel intake spigot horizontal underslung below the fuel-air- mix intake column which runs aft from the engine’s backplate. I have made a 3/8” diameter hole in the fuselage side, close behind the firewall, for the needle valve  to exit, and a 3/8” hole on the other side for the fuel line to enter, from an eyedropper tank, or from a similar tubing coil tank. I have removed the nacelle “cheeks” and may taper the fuselage nose to fair into a round firewall which is the same size as the backplate. The firewall will be exactly where the plan shows the engine backplate in its illustrated cage mount installation.The pylon will have to be re-located aft so that the cg will come out right.
The hole in the firewall is sealed by the backplate of course and admits no air. I am wondering how much additional air entry I need to allow beyond the (partially obstructed) 3/8” holes.
It seems advantageous to place a balsa bulkhead some distance behind the firewall, quite close, in order to minimize the area exposed to fuel and for structural reasons (except that it might e wise, for the engine’s sake in a crash, to not make the nose too strong). I am wondering whether the resulting compartment might lead to resonance which would impede air intake and whether one really ought to put the bulkhead 2 to 3 inches back instead of just beyond the venturi. Of course some slipstream exhaust oil and fuel would get into the air holes so that the compartment cannot be expected to stay 100% dry.
Also I wonder whether anyone knows how much fuel might be blown out of the venturi and leak from around the needle valve, with respect to fuel proofing inside, and to cleaning the compartment with a Q-tip, talc, or however.
Might an air intake scoop be preferable to flush holes? Perhaps the Bernoulli effect might create suction above flush holes since the airflow would speed up when going around the fuselage nose?
Especially with regard to the bulkhead placement it would be helpful to hear from practical experience since it would be difficult to re-locate after constructed. Could one usefully make a ½” or ¾” hole in the bulkhead and run from it a large diameter straw back to a beveled exit hole in the fuselage side or bottom some distance aft?

its like a smal sportsman tink best is keap ventury inside engine compartment y try sort of Intake like on sur start engine it work fine tink is Not best