"http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXZ653&P=7"
I have that muffler and it is great. I also had the tower trainer as my first plane, its a great plane and very forgiving. Also as far as GC is concerned remember its OK to be a little nose heavy, but never tail heavy. By the way, I used an O.S. 46 and it was almost spot on.
Glad to hear it flew. I bet it was your elevator servo that was reversed wasnt it? I did the same thing when I was building that plane.