I talked with a guy that ran the RCS 140 on the Ultimate and this is what he had to say...

Good choice on the engine. Its a great little motor, you will love it. I sold my ultimate about a year ago. I didnt do any extra bracing for the RCS. Its not needed. I used the stock RCS muffler. It is a smoke muffler although I didnt use a smoke system. The engine was mounted inverted. The elevator servo was mounted behind the canopy on some cross bracing and the rudder servo was mounted in the stock location above the landing gear. It flew fantastic with the RCS, awesome vertical and it would hover at 3/4 throttle. I mounted the fuel tank over the CG on some cross bracing. The stock fuel tank location housed the ignition module. I used a 10oz dubro tank for 15 min flights. here are some pictures of the engine and airplane.

Looks like I am going with theRCS 140 also!!!