Thanks all. I ended up finding a D950 that I could check out in person. It had good compression and oil pressure and a water pump, but it was from an Onan marine generator.
It took some creative work to get it to fit (different timing gear cover - had to be trimmed to fit the front frame, oil filter on the other side of the engine that interfered with the front frame - solved by adding a remote oil filter, no PTO out the front - fabricated PTO shaft that bolts onto the front pulley, different cooling hose size and locations - had to make a crazy pipe assembly to use the use the old radiator, different flywheel - swapped the one from the D750.. oh, and all the studs in the head had to be transferred due to different lengths... and swap oil pans and sump pickups). I'm REALLY good at taking off/putting on the head and oil pans on these motors now!
Initially after figuring out all the differences and realizing that my original plan to swap the timing gear cover from my D750 onto the D950 wasn't going to work (950 has a passage into the block for the water pump that the 750 cover wouldn't, well, cover), I had tried swapping the D950 head onto my D750. I had put in new rings, but it really needed new liners as well. The valves in the D950 head are larger and it was too finicky for comfort to get the head lined up so they wouldn't rub on the cylinder walls... It was a comedy of "this should work... uh, nope. try this.. nope.. try that... nope... now what? Can I return the D950.. not really... now what? What if I... yup... this should work. I just need to make a... now what?. In the end I managed to make it work without any modifications to the tractor frame, so I can always return to stock if I trip over a good running D750. For now it's all put together and running and I'm happy. The only thing that's a little funky is the injection pump governor for a generator is set up for much tighter speed regulation - most diesel governors are a bit "softer". When I let out the clutch or load the motor it doesn't slow down even the slightest bit. Changing throttle position results in instantaneous response. This makes it a bit jerky. I may try adjusting it or swapping the governor guts out of my D750... someday.
So.. I've got $150 worth of new rings that I can't return because I installed 'em in the D750 before deciding not to go that route. (It isn't worth the ~$400 to replace the cylinder liners in since it also needs a new head). I've also got a D750 head gasket that was torqued down but not run, and a timing gear gasket for a D750 that won't fit my D950. Anyone interested in a good deal on some almost-new D750 parts?
