rreiss
There's some bs floating around about moment of inertia if the engine is out too far. If you drill the front holes about 1/4" from front of mount, it'll be fine. I still had to use a heavy Higley hub inside spinner to get a 4 1/2" cg. I had a TT 46 to go in it, but I didn't want to cut so much of the side cheek for the exhaust, which lead me to the TT 54 4c.
For starts, don't go past the 4 1/2" cg. Too many expert pilots are suggesting rearward cg to intermediate pilots. Not many average pilots can fly helo-planes.
I mounted my engine way out on the nose. I did that last so I could adjust it depending on balance. I held it in place with a few rubber bands until I got it right. I have my battery just behind the tank by the receiver.
I agree with you on the 4 1/2" CG for new Twist fliers. Any further back and the plane will balloon on landing when you get slow. Most people would think that you need to just land faster, but this plane won't quit flying when it's going fast.