On my 95 IH with AmTrans body, the first window came out with 4 screws, then the next one came out with two. Or you can look at it this way, after taking the first two screws out, depending on how many more you wanted out, just keep on taking two screws at a time.
Never heard of a quiet bus window. I drove mine back from Nebraska and they really tested me on patience.
As for as locking the back door, i drilled a hole through the back door, installed an eye bolt, and drilled a matching hole in the handle. It keeps the honest people honest. If they want in your bus, they'll find a way in.
95 IH 72 passenger transit school bus w/ DT466 and 545 Allison.
79 IH Scout II/392 (0.030 over) Hamilton Injected/727/D300/Full size axles/36" Swampers/Lockers/OBA/38 gal Custom fuel tank, roll bar, tube doors.