Just finished installing a Triangle kit in my 2013 900. I have the L & R rear glass and as stated you have to space the bracket out a quarter inch from the mounting location or you will be pressuring the glass panel. I had issues with the bracket making too much contact with the bed when I spaced it out so I ended up drilling new mounting holes in the supplied bracket to raise it up higher taking advantage of the brackets angled rear face to get the clearance. Had the bracket on and off 3 times before I was happy with it. The video shows two people installing this bracket and I recommend that. I did it by myself and you need 4 hands it seems to get it done. My Ranger has that additional plate they say is on the 2014 model making access to the two mounting bolts near impossible. Triangle should have added those thin washers that thread on bolts to hold them in place temporarily while you are assembling this unit. Their idea of using electrical tape to hold the bolts is not a good solution when by yourself. I ended up welding the bolts to the bracket and that helped immensely on my third assembly.
Regarding the intake hose with the duckbill in it I suppose you could head to Home Depot and find the correct size fernco (rubber) connector to fit the air box. You would have to bring the air box flex hose right up from the box to the triangle bracket without going into the cab. I think you would have enough flex hose for that. If not H.D. sells that kind of flex hose for hot tubs, might not be black but I know I've seen it there.
Here is what I mean to keep the bolts in place - they are called push nuts https://www.fastenal.com/web/products/details/0162862
Another suggestion for mounting the bracket on the inside. Triangle supplies two big washers to span the channel inside. The washers quickly fold in half just about when you tighten the bolts. I used an 2" wide X 4" long piece of flat stock and drilled two holes in it to slip over the bolts, I used the holes from the supplied bracket as a template. Much easier to handle and more secure when tightened.