I'm have several problems with a 8.3 Cummins in a White 4-210 tractor. Did a overhaul on it last fall. Sleeves and pistons, New head and injectors and put a new radiator in as well. Right off the bat the cylinder head had a casting flaw oil would pour from the side at #2. Turns out there was a flaw where the front bolt on #2 rocker assembly allowed pressureized oil to get to the out side behind the injection pump. They would not stand behind the head so I fixed it with JB weld using the bolt to force it out the flaw then re-taping. Didn’t like it but its all I had time for and it held ok. From the start the tractor ran hot under 1/2 load or more on warm days 70F or so. When it was below 50 it did not bother but would not stay warmed up if you left it idle. I changed the thermostats 3 times and tested them in a pot they work as they should. It will intermittently push coolant out at full throttle hot or cold and when I drained the coolant to replace the thermostats the pails would have black dirty water in the bottom each time. I flushed the system and used new pre mix antifreeze each time. Could not find any thing wrong with the water pump and the water circulates freely when it's hot looking in the radiator. Temp sender checks out ok. Timing is correct. Never smell coolant in the exhaust and never loose any. I took it in to the local shop. They pressure tested each cylinder with shop air 120psi all held ok. I had them pull the head anyway and discovered the exhaust manifold was wet to #5 and 6 with raw diesel setting in the piston crater on #6. I never noticed it miss. But they said they kind of noticed it. Figuring a bad/stuck injector I took them in. They checked out. Valve clearance was ok. Liner height is in spec with no scoring. Head gasket shows obvious sign of leakage. The only problem found on the head is it's warped .004 the shop wants to surface it and reuse it I don't know that I want to do that. Engine had very little blow by. What could cause the raw fuel if the injector and cylinder are good? Any ideas where to go next? Thanks