FB,
I'm not sure of the dimensions of the EVO 33 as they might be a little different from the 35GT (turned into the 40GT a little later on). It LOOKS about the same, but the older 35's didn't have the rear mounting lugs, just the beam mount. Anyway, if I would have used the wrap around muffler, I would have either had to move the engine pretty far forward with the carb sticking out of the cowl, or modified the lower front of the fuselage with a cut-out for the muffler as the fuselage sticks into the cowl quite a bit.
I'm not much for mufflers sticking out either, but I didn't feel like doing all the work to get the wrap around muffler to fit, after all, it is just a fun fly ARF. I also added nose weight, but I don't remember exactly how much now, I think somewhere around 8oz.
One thing I did do, and I'm sure I hear a bunch of negative comments about it, was added a gyro on the rudder. With the narrow gear, it can be quite a handful on takeoff and landing. With the JR370a gyro onboard, I could straddle the centerline of the runway and make a nice straight takeoff (I fly off pavement), while another Stagg at the field would be all over the runway before getting in the air. I can hear everyone saying "Learn how to use the rudder", well, I do know how to and I'll bet they have never flown a Stagg. One of our club members owns a full scale Stagg and he says even that one is a handful on take off and landing.
Even thought it requires your attention while flying, it is one of my favorite planes, so much so that I have a spare one new in the box.