Anyway to tell if engine has been overhauled?

Im looking at buying an 06 Kenworth with a c15, 13 speed, and 1.4 million on the clock. It's rated at 550hp and is putting 485 to the ground on the Dyno with 3 inches of blow by using mercury. There is no motor history on this truck. Myself and the dealer have both tried tracking it down but the previous owner has passed away. The truck is about as clean as they come. The interior is #### near like new. Of course it don't matter how good the truck looks if it won't drive down the road lol. Im wondering if there is anyway of knowing with any certainty if the engine has had an in frame? Also, what's the typical life span of a 13 speed? I like the truck, and id like to buy it, but I need to make sure im putting my money in the right place. Thanks for any help.

 

This is the best I have right now.

 

Dealers usually always blast and reapray the frames on useu trucks.

 

Would a c15 with 1.4 million on it still be putting out 485hp to the ground though?