The GM is a newer version but very similar to the QM. Differences would be in the governor, QM has rocker towers, where GM has a rocker bar. Both pushrod diesels, so the GM will be a fair guide to the QM as to remove and replace. Same basic
engine design.
The QM is in my mind the better
engine, with sleeved cylinders, lower peak
RPM and generally heavier construction.
Parts are becoming an issue, but rebuilding pumps and starters, injectors are done all the time. It should run a long time.
Of course changing the bearings in the
water pump">raw
water pump (easy) and
water pump (less easy- needs a press) and replacing the discharge
elbow would go a long way to reducing surprises.
Best of luck with the QM.