Great info Dave. What year were the cut-overs?
As my Grandpa used to say - "I asked what time it was and you discribed how to build a watch"
The Gen V was first installed in the 1991
The earliest casting I've decoded was a very late (Nov/Dec?) 1989 date.
The Gen VI was first installed in the 1996
The cams for the Mark IV and Gen V are interchangable for flat tappet lifters.
The Gen VI where the first equiped with Roller Lifters, but the main difference is the machined flats on the lifter bores of this block - you can still install an earlier cam without rollers.
The cam retainer plate holes are verticle on a Gen V~VI, rotated 90deg from the Mark IV's horizontal orientation.
The '91 on trucks with Gen V's had manual transmissions and use a bracket for the pivot, the later medium duty trucks have a hydraulic clutch.
The Gen blocks use longer main cap bolts than the Mark blocks.
The crank on the Gen engines uses one long key in the keyway slot for the cam drive gear and the damper - the Mark cranks have two short keyway slots and two seperate keys, one for the cam gear one for the damper.
As he stated, Gen cranks are one-piece seal, Mark are two-piece.
The Flex plates are interchangeable - but Flywheels, for truck and marine applications, are not interchangeable on Mark and Gen engines.
Hope this gives you a better watch;