A 8.3 ISC turned up to 350HP will be lucky to make it to 500K miles, but one making 250HP or less should make it without any major problems. They know we are not going to put that kind of miles on a MH so like fire trucks, they sacrifice longevity for power.
Unfortunately the OP did not keep his old parts as I was serious about buying them as that is how certain I am that he got had. With all of those problems, how did it even make it into their shop without overheat (pressure leak) and the turbo not working well enough at 5000'.