871 sludge in oil

[Nostalgic]

Based off your copper and lead, dropping the pan and inspecting a couple mains and rods would be a start. You are more than likely ready for a rebuild. Running it that long with coolant in the oil ate away at all of your bearings like sandpaper. I'm kind of surprised you didn't spin one and lock it up.

I typed this BEFORE I saw your copper and lead #'s.

I'd determine how and what to use based off of the sludge I could see on top of the head. Does it dissolve when you pour diesel on it? What about motor oil? Or does it stay chunky? Is it liquid feeling between your fingers, or more like grease, or clay?

No matter what method you use, you risk spinning a bearing somewhere if it starts to break up and plugs a bearing galley unless you find something that instantly dissolves it.