The engine is a standard GM truck engine. There all sorts of different manuals available from shop manuals for professionals to DIY manuals like a Haynes available at places like NAPA or CARQUEST.
As far as manuals for the bus body, they are available from Blue Bird. But as one that has tried to use them in the past, most of what is in the body manual is pretty common sense and not worth the $$$ if you have to pay for one.
Almost everything Blue Bird used to make your bus is pretty easy one-size-fits-all stuff. There is very little in the way of electronics that you will use in your conversion and nothing is multi-plexed so wiring is pretty straight forward and simple.
When you open the panel to the left of the driver there should be a schematic of the wiring glued to the panel door.
If there isn't one there your best friends are going to be a 12-vdc test light and a mulit-meter that will let you know if you are have continuity.
Even if you have a schematic it doesn't necessarily mean that is the way in which your particular bus was put together.
Good luck and if you have any specific questions please let us know.