I believe you meant 350 C7 Cat engine. You probably have the Freight liner chassis and the air filter is on the driver side next to the rear cap. I have changed the filter on mine about four times since I bought the coach in 2003 and you release the two clamps holding the air cleaner, loosen up the clamps on both ends of the air filter. That is the hardest part breaking the rubber hose away from the filter. But other then that it is fairly easy once you get the trick as to how it is done.
You can order the filter through the internet. I found out that my Caterpillar engine runs much better with Racor air filters. It has all kinds of power with the Racor.
2002 Gulf Stream Scenic Cruiser
330 HP Caterpillar 3126-E
3000 Allison Transmission
Neway Freightliner chassis
2017 Buick Envision