You seem to quite well versed in those areas so I will tell you in detail about my 350's symptoms, and what led it to where it is right now: Still unknown problem, but lack of compression.
I first posted in August of 2003.
http://www.peachparts.com/shopforum/showthread.php?t=73746&highlight=stage+engine
It appeared that the oil consumption and the rough running had been reduced substantially. It wasn't perfect, but I remained optimistic.
That winter, the 350SD started in -10 degree temperature with a 30 below windchill factor. No block heater, and one 30 second cycle of the plugs.
Later on I posted about my new issues with consumption had then become visible.
http://www.peachparts.com/shopforum/showthread.php?t=111514&highlight=350SD+oil+consumption
http://www.peachparts.com/shopforum/showthread.php?t=111512&highlight=350SD+oil+consumption
I am down to this: Either a cracked piston ring or bent rod ovaling out cylinder. I know when I put a commercial product called "SMOKE-B-GONE" compression restorer, the car was soon back to it's original shape: No smoke, less oil consumption, and a smooth idle.