Congratulations, they are getting harder and harder to find.

Regarding the YS 1.20 installation:
I have a YS 1.20 in mine. No real need for a pipe, and it would be hard to locate it in the belly pan. I use the standard muffler and vertical performance with a 14 X 10 is unlimited. I used the included stock soft mount, locktited all screws and nuts on it, and so far have had no problems with it. Some have had theirs break, and have opted for the very similar but more robust MK soft mount assembly.

Regarding tank location:
The stock tank fits with just a little modification inside the middle fuse former that happens to be right over the CG. With typical throttle management found in turnaround pattern flying, this 12 odd oz. tank is good for 20 minutes. I used a Velcro wrap to hold it in, and my 1700Mah battery is velcroed under the back one half of the tank, right in front of the elevator, rudder, and throttle servos. Had to add one and a half oz. of lead to the tail to get the CG suited to my tastes... without the lead knife edge seemed to require a bit more rudder than I wanted. The tail weight made the model neutral, at least for me.

Radio Installation:
Once again, the design is good enough so that I went with the stock pull-pull, running it through the little tubes which are pre-installed in the fuse. At first I didn't think this was going to be a good idea, but many flights later, the pull-pull is just fine. Some flyers like to cut the counter balances from the elevator halves. There is a thread in the forum which discusses this.... hope this helps.

GPB