coolant change on d6-9u

Mine has a stainless steel hex head stem. There is a hole in the side shield/brace for the hard nose to stick a socket on a long extension through.

It would be a long shot, but there is a crude fuel/coolant heat exchanger at the top front of the fuel filter tower. Of course that would be fuel not oil. There is a pretty robust cast iron separation there, but could have a porous casting or crack from freezing in that area.

Any coolant in fuel or oil? Compression pressure in radiator? Overheating?

The oil cooler is completely independent of the engine cooling system, not likely to be a source there.
I would tend to suspect the head gasket but to get really black scum, (combination of soot, oil, and fuel) getting by a low liner, possible crack or pinhole. Do the bubble check for compression leak at the radiator neck.

thanks Magnet
on the bubble test do u mean check at the large screw off top? or remove the plate where the radiator inlet hose enters?
at the top of radiator im getting no bubbles but u can see the water swirling and moving. Oh and an update on the drain valve. the impact gun didnt work. i guess to many years of nonuse. i can open the block peacock so im going to drain flush and repeat until i get clean coolant to drain.

Bubble check is just with the radiator cap neck full.
Depending on your s/n there is another plug (npt) on the same pipe as the drain valve, might try opening that one but they usually are just about frozen up.