So, my friends just recently bought a MC-5 from a church and it has an 8V-71 in it. There were able to drive it to storage and then drive it around a bit, but now the bus will start and then it will blow lots of smoke and wont go past 900 RPM. I don't know yet what color the smoke is or how long the bus sat without the motor being ran, but I from what I know so far, I don't think this is good news at all.

Anybody have any knowledge on this or know where I can go for answers?

I'm not a diesel professional, but those Detroit motors are in a class to themselves. I don't know if it's low class or high class, but there are people on both sides of the dividing line. I'd hit up a diesel-specific board (am I allowed to name them here?). Search Google for Detroit Diesel Forum and you'll see the first result is Diesel Stop. I'd start there.