Might try testing the oil (sending a sample to a lab), I don't know that it would tell you a whole lot since you don't have a baseline of tests, but it could tell you if there are bearings that a wearing badly... I think there are a few guys that test on a regular basis so they could tell you if things aren't normal when you got a report back. The lab will probably have seen a few samples from a 617 engine before too. At the very worst it'll cost you the $20 or so you spend doing it.

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1985 300D Turbo ~225k
2000 F350 (Powerstroke) 4X4, SWB, CC, SRW, 6spd ~148k
1999 International 4900, DT466e (250hp/660 ft/lbs), Allison MD3060 ~73k