Have you checked with Kevin the azdieselman here on the board do like I told you buy the test kits from Empire pull samples on the coolant,oil,rear gear and,transmission ,check for cracks and welds, sloppily steering,uneven tire wear If the guy checks the turbo,pulls the air box inspection covers and checks the pistons and rings for wear that is about all one can do to check the engine,the jakes will be a minor problem, it's a roll of the dice Scott this is why I don't do inspections on 50 +year old buses. A 1000 bucks may save you 15 to 20 grand on the engine alone but I would be sure he knows the 6v92 good luck
60 to Globe would be a better test once you leave AJ it's all up hill on a 2 lane road most places