What engine are we talking about here, losing coolant, overheating in the past, and pressure in the system after cooling all point to head gasket... Any water in the oil?

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1987 300TD Turbo 5-spd
1991 350 SD Turbo (Frankenstein 603.970 crank, rods and head on a .50 bored 603.963 block )
1982 300D euro 617.951, 4-spd
2003 E500

2000 GMC C2500 6.5 TD (Double ott, ex DOT truck)
1980 Scout Traveller SD33T (Resting!)
1997 GMC K2500 Burban 6.5 TD (mid engine rebuild)