Youre better off using a mousse can instead of a macs muffler. They can be very very finicky to tune for transition, either running too lean on the low end, or too lean on the top end.
I braced my tail with wires, and I'd say it is a necessity. Look at the area of the vertical fin compared to the rudder. Then look at the small area youre supposed to glue to the fuse. It needs all the help it can get.
I ran a 4 cell 720 nimh battery pack from
www.radicalrc.com, and had it stuffed about halfway back between the TE of the wing, and the LE of the tail. I also had about 1/4 oz of lead on the tail that I could take out on reallly windy days.
I had my cg right around 5 1/4" or so from the front of the wing. Any further back, and the tail would squat really bad. I could get fuse length waterfalls using high rates and flaperons, and incredible flat and climbing spins. I'd start out about 4 3/4- 5 inches, depending on your funfly experience.