What year is your bus? I have a 2000 GMC with a Bluebird Body on it. You should know that the GMC part is a GMC Savana 3500 Van ... it might be easier to get parts if you give the parts guy this information.
You might want to read this regarding the 6.5 engine. I think you may find that the problem you experienced is caused by a failed PMD/FSD (Fuel Supply Driver)
Make sure to read through the entire article, especially the part about harmonic balancer failures and head gaskets.
6.5 NEWBIES - **START HERE** - Diesel Place : Chevrolet and GMC Diesel Truck Forums
BTW, its probably a good idea to register on that website ... you'll find answers to almost all of your engine questions there.
A lot of folks think that the 6.5 is a "bad" engine, I agree with the author, it IS an engine with a couple problem spots but you can avoid an engine disaster if you take a couple precautions.
When I bought mine, I was aware of the weak spots, so, as soon as I got mine home, I replaced the timing chain and gears, the harmonic balancer, Valve cover gaskets, front engine seal, water pump and thermostats and hoses. It's a lot easier replacing these parts as "maintenance items" and doing them all at once is actually a lot cheaper than doing it piece meal, and certainly better than snapping a crankshaft out on the road.
My bus: http://www.skoolie.net/forums/f27/b-...t-b-12458.html