ORIGINAL: kdheath
Couple of easy things you can do include drilling out the venturi as much as possible. I'll have to look and see if I can find the size it will tolerate again, but the info is out there.
Bear in mind that the larger the intake the less the fuel draw. Of course you can run a baloon tank for pressure.
Then find a dual port (TeeDee) piston/cylinder set.
I do not yet have my new ones, but one from the Nabu Fighters already has two port transfer, including the boost port found in the TD. It has the two slit exhaust ports with no sub-piston induction.
Try smaller props like a 5/3. A balloon tank is probably the best choice for consistent running. And be sure the piston ball socket is snug. Use a reset tool if it isn't free of slack. Still won't be as good as a Norvel, but much better.
I would also suggest 25% nitro, various props (perhaps a 6x2 might be good for that plane), vayious quantities of head shims, especially if trying the TD (fluted?) head. I think Cox still makes two other heads, the conical (standard), and high-performance (smaller cone with squish band). You may also want to try the Norvel head/plug and the Galbreath head/Nelson plug.
That's a lot of testing for an RTF, but some of it will probably make your Viper Hyper.
George