1991 Other Chevrolet Models 6.2 diesel malfunction

I was driving my truck yesterday when all at once it felt and sounded like someone turned on the Jake brake. While it is a diesel my truck doesn't have an engine brake. I stopped the truck and shut it off. The belt had slipped off but I didn't see any other damage. I tried to re-start the truck and get it off the road, but the engine, which still sounded like it had an engine brake, died after 20 feet. I got the truck pushed into a parking lot and noticed fumes coming from the air cleaner. The intake was full of atomized fuel. The one explanation I can think of that fits is the timing was thrown off. I don't think this engine has a timing chain but a gear driven cam and push rods. Where should I start? Correction, my engine does have a timing chain. What is the correct procedure for base timing the valve train?