Custom patriot and webra 120
The webra 120 is a long stroke engine, it's meant for torque not RPM. 8800 is probably about all you'll get. You'll get a little more speed if you up the pitch of the prop, say a 13x13n or something, but you're not going to get mucy RPM out of it. I ran a webra 120 on a Pipe using 25% nitro on a 14x10 and got 9200. Not enough to warrant the extra weight of the pipe.
If it's only 12 pounds though, I'd take that boat anchor off the front (I never liked my webra 120 much) and put a JETT90FIRE on it. Or even put an OS91VRDF ducted fan engine with a prop on it, at least then you'll get some RPM's. 12 pounds isn't heavy for a jet, and with a propjet you'll have WAY better thrust than with a ducted fan.
Even try an APC 12x13n or something, or 12x12n (the n is for narrow blade) I think they even make a 10x12, but the thing is, this engine is not designed for high rpm, if you try to rev it to fast you'll just blow it up.