Well, I'm doing the best I can to be an effective detective on my end. The ideas and perspective y'all offer do indeed help.

I'm quite sure it's not gummed rings. I have done a cylinder soak over the course of a week and it did not alter the compression numbers. That said, I believe the engine should fire with the compression it does have.

Water injection is not helpful because I can't get the engine to fire up. i am intrigued with the idea, but at the moment it is irrelevant.

As suggested, I flushed the IP by dropping a line from the lift pump into an acetone bottle. I removed the return line from the injection pump to the diesel filter and replaced the check valve with no hose attached. This video I shot today after having cranked a little every day for a week to flush the acetone through little by little. Some gunk did come out, perhaps I just need to run more through? Anything better than acetone? I also cleaned the delivery valves and fitted new copper washers because a few were leaking a little. Now the pump is only firing from line #5. I'm not sure what to make of it.

Here is the video: https://drive.google.com/file/d/1VTXZXNZG_5f96WM6sfLzFpr07mv5rRu3/view?usp=sharing