The TT120 would make a good choice. Good engine, will give you pleanty of performance.

From a CG standpoint, Im not entirely sure why others have had to add so much weight. A local one flying here is flying with an OS91FX and the scale exhaust - balanced pretty close with the battery pack up on the firewall. Flys pretty well.

But there is a lot of experience in here with the Bear, so I will not by any means discount it.

I did a fit-up for someone not long ago for a Jett BSE-120 and turbo-jett muffler installation. Fits in there perfectly. Engine is the same size as the TT90 and OS90 the plant was designed for, so it drops right in. Turbo-Jett fits nicely in the cowl. He expects to run one of the Supercool 16x9 AT-6 racing props (clipped a bit to about 15" dia - get up to around 11K rpm).

[link=http://www.jettengineering.com/hall/at6com.html]info page on the AT-6[/link]

Da Bear is about the same size and load as the AT-6, flys in about the same speed range - should work pretty well.

BTW... there is no model 4-c engine that sounds anything like the full scale Rare Bear. Lots of cylinders firing with every turn of the prop. Such a sweet sound too.

I hope this is helpful
Bob