There should be a line setting ticket somewhere on the bus. If it isn't there any longer you can get a copy of it from any International/Navistar truck dealer or an IC Bus dealer.
The LST should be stuck to the hood just above the hinge on the curb side. If it isn't on the hood look for it on the fire wall. If it isn't there look on the kick panel just to the left of your left foot in the driver's compartment.
The LST will tell you everything about all of the parts and pieces that were used to make your chassis.
There should also be a sticker on the side of the engine or on top of the valve cover that will have the engine (DT360, DT466, etc) and HP rating for that particular engine.
Rear end gearing should be noted on a metal tag attached to the rear end on the top curb side of the back of the rear end.
There may or may not be a builder's tag on the side of the transmission.
If it is a 5-speed deep low is up and to the left, the first gear you would usually use, 2nd, will be up and to the right of deep low. 3rd gear is straight down, 4th is up and all the way to the right, and 5th is straight down. Reverse is all the way to the left, push against the detent spring and then down.
If it is a 4-speed, deep low is up and to the left, 2nd gear is straight down, 3rd is up and to the right, and 4th is straight down. Reverse is all the way to the right, push past the detent spring, and then up.
Brake parts are available from any IC Bus or International/Navistar Truck dealer, NAPA, CARQUEST, and any other parts house that caters to medium/heavy duty trucks.