In a perfect world, a well-rebuilt engine with a prelube system to prevent dry starts and conservative EGT's that isn't lugged or run above redline will last **** near forever.
The consensus seem to be:
(Re)Build quality and oil starvation on startup are extremely important to engine longevity. Build quality can't really be checked without knowing exactly when/were it was rebuilt, or doing it yourself... or having it fail with low miles/hours resulting in the opinion of "MF engines suck!"
Installing a pyro (preferably pre-turbo) and optionally a boost guage makes turning up the fuel much safer. Didn't someone mention that the rear side of the manifold ran a bit hotter?
With a pyro, start cranking up the fuel a little bit at a time until you see black exhaust or temps that make you nervous. Disclaimer: this is on long, sustained pulls- not idling in the driveway.
For diesel power: lower CR to avoid high cylinder pressures at max boost, more air, more efficient turbo, better oiling for internal cooling, and less exhaust restrictions. Last item's not a problem for us.
It seems we really can't run a post-turbo intercooler on a MF due to the water-jacket's design.
Lower CR removes that whole "MF" feature- Heavy Hooker's comment about -1D pistons causing cold-start issues would be even worse on WMO, for example.
More air is a big thing for MF's- the stock air cleaner was made for a gasser. Grab an air cleaner from a tractor-trailer and see if it runs better. Turbos seem to be either small and responsive, or big and free-flowing. Someone who's name escapes me mentioned using a housing that better matched the turbine to get better performance.
Better oiling? Get an LDS. I don't know if anyone as ever tried adding LDS features to an LD/T block.