Not to be argumentative, but I think there have been many other diesels built which were worse than a 6.4L. Does anyone remember the Gm 5.7L?
I rented one a few weeks back for a diesel drag race at Indy. Bone stock I was running mid-15's.
Sounds like maybe an injector was stuck open and dumping raw fuel, probably washed down the cylinders, and the now-contaminated oil could have screwed up many other items. The excessive smoke was likely from the stuck injector, and this would have nothing to do with oil change interval.
You might want to post on a Ford Diesel specific web forum, like:
www.powerstrokenation.com
www.powerstroke.org
Regards,