Yes, replace the rudder hinge w/ Robart Point Hinge, and use 3, making sure 1 is as close to tail gear attachment point as possible.

I had experimented quite a few engines on my Flip:

*Magnum 52 XLS 2-stroke: plenty of power, but doesn't quite cut it due to louzy transition

*OS 70 Ultimate: adequate power, good transition, but could use a little more. This engine has design flaw from what I've read.

*Saito 82: perfect power, swinging APC 14x4W @ 10700 on 30% nitro fuel. My only gripe w/ this set up is that the 82 vibrates a lot @ 1/3 ~ 1/2 throttle, and the Flip w/ its clear Ultracote tends to resonate greatly @ this rpm. When I hover, the ringing vibration makes me uneasy. If you can, try APC 15x4W instead, as it will peak @ Saito 82's power band better (mid 9k).

*Saito 91: awesome combo; it will waterfall forever w/o dropping. APC 15x4W @ 9800.

The stock landing gear may be too short for 14" or 15" prop. You might want to look into Fiber-lite's gear for Something Extra. That's what I used. Just don't point your exhaust to the CF gear.