The rear end of an RE bus is turned around so it is turning opposite of what a FE bus--nothing special except the housing has the vent relocated and the cover may have the logo upside down with a second fill hole.
GM buses that have the V-drive have 2-cycle Detroit Diesel engines that are left turning instead of right turning. Why they did that I have no idea since it would be have been just as easy to turn the rear ends around as it was to have the engines turning backwards.
Some buses like the Flxible FlxLiners and some of the Eagle buses have drop boxes that change the direction of the engine. The drive shaft goes over the top of the rear end into the drop box which then turns the rear end that is facing the front. The use of the drop box allowed for longer engine and transmission packages without increasing the rear overhang or wheelbase.
Some low floor buses with front engines have used drop boxes in order to get the driveline low enough to clear the lowered floor. Some have even used a drop box in the front and another drop box in the rear in order to get the driveline low enough. In those buses when the air suspension is lowered into the kneel position the driveshaft is almost touching the ground.
No school bus to my knowledge ever used a left turning engine or a drop box.
I found a flashlight and fishing pole handy. It got late and I wanted to stop occassionally and check things out. I used the fishing pole to stick down into the fuel tank to confirm what the gauge showed and to make double sure that I had fuel to get down the road. Don't take a stick or thin dowel. I used a dowel the other day and it broke in half. Now I have half a dowel in the fuel tank to fish out someday. Oops.
Okay so I ended up getting pretty lucky. While I have yet to move the bus to its final destination while I convert it, I did manage to go look at it and get the title. It ended up being almost completely rust free with an at545 transmission and the 5.9 cummins.