Heres what I did for a filter. I had an extra honda trx400ex k&n filter laying around from my race quad so I just removed the air box on the lifan and ran that filter. I cant remember if I made a rubber boot for it or if I just duck taped it to the air boot but it worked. But remember if you change the intake or muffler you need to rejet or you will go lean.
For the exhaust I just pulled the inside out of my muffler. So it was all hollow just the canister. Then I put a 2" flex pipe inside it to make it work just like a aftermarket exhaust.
Or you could do what I did last. Ripped the engine out and since I build race quads I had a yamaha yz426 engine that was built for national racing and put that in the bike making it the worlds fastest lifan lf200 50+hp vs16hp stock!