I think your compression rings are carboned up from the unheated vegatable oil. The same gummy stuff that was on your glow plugs got down there and baked on.
I agree that you should try the marvel mystery oil for a soak first. Let it work for a few days adding a little more each day. I do not know what that marvel mystery oil is actually but I hear it reffered to fairily often.
I too have an engine that was run on unheated vegatable oil. It did not get as far down into the mud as yours has. Thats primarily because my car broke with another problem first and he walked away from the car. If that had not happened I imagine it would have been fed the same diet until the engine did not have enough compression to start at all. In your case I think he tried until he burnt the glow plus out.. Usually they total the starter.
I might pull the injectors to see if the prechambers are gummed up as well. Expect buildup on the nose of the injector and make sure those holes at the bottom of the pre chamber look clear.
I hope the mystery oil softens up the carbon around my rings as well so I do not have to take more drastic measures. Mine did start with block heater applied for a couple of hours. The engine had not run for at least a year as well. Glow plugs were fine. It would not start otherwise and it was not cold.
Before that I drained and changed the tank fuel. Still had to start on the vegatable oil in the pump and run through a little of that first though.
I guess I could have power bled the pump out by loosening the injector lines and cranking for quite awhile.
I was able to pump up the new fuel with the hand pump. So the bulk of vegatable oil in the lines and filters was mixed with the diesel fuel in the tank as it was driven down the return line. Keep us informed as to how things go. I hope these situations are salvagable. I have mine sitting at present and will not be going near it again for a few months yet. I have been waiting for other victims to post attempts at cures and pick the best ones out. Although I have done little research myself yet.
More information on this problem is on various vegatable oil boards. It is one of those things that has to happen to you to really appreciate. Unfortunatly my car is a real fairly low actual miles car. I also suspect this carbon cannot be just driven out. It will have to be broken up and expelled or dissolved before those upper compression rings can work well again. Unless they are already damaged somehow. I would not be concerned about any smoking tendencies the engine has at present.
My engine also at present has the most actual blowby I have ever seen in a running car. And I remember well the old cars years ago that went though a quart of oil every fifty miles. My blowby is primarily combustion gasses rather than oil burning. It is pretty clear but has a lot of pressure behind it.
There is sort of a bright side . If the cars had not been burning unheated used or new vegatable oil we would never have got our hands on them cheap. Plus I suspect your injection pump is still good. That is also another large plus. It is the second most common reason unheated vegatable oil burners become surplus in my opinion. I personally have no bias against running vegatable oil as long as it is done properly.
Your compression numbers do not alarm me at this point. Might if that carbon does not come out though. I suspect the compression rings are cemented in as far as the lesser taper of the lower area of your cylinder wall allows. I will be watching your thread.