Can you carry a tune with that air box? Most people realize that the intake is tuned like the exhaust not to reduce sound but to tune the intake for better
Engine filling, I bet your best performance will be with the factory air box installed, if you butcher it up and use your version you might even loose power, some place I read about tuning the intake but don't remember where I will have to do some searching, I could not comply with the rules they were using on my Pilot because of room constraints so never bothered to pursue it very far, now my setup has changed with the installation of the 440 Engine perhaps I can use it, hmm, you should have laid the transmission down like on the ATVR Taz car and mounted your Engine up when you did the Engine mount mod, then that air box would probably fit right in hehe, I know that would be rebuilding the whole car, gas tank, pipe etc.....
The horn is like the tune port on a speaker if I remember right.. It has to do with resonate frequencies and all kinds of other stuff I don't understand, you can bet ski-doo spent some
big bux engineering that to work on the sled.
Muffler looks like a tool capsule