Yes, you certainly will get it running again. By that added bit of information, that it sat around and is/was gummed up, should direct you to the problem and to me since your pumps are done or almost done apart from a leak, the obvious place to me is in the injector itself. Only a total strip down and clean then assembly and setting it to the correct pressure will we all know whats going on. But you have worked your way through everything else so you must be close by now.

Have you pulled the i njector and physically seen how much fuel is coming out of the nozzle atomised? With out doing this there is no way of knowing how much fuel is going in.
If you wish  not to try a bit of either then squirt some oil into the cylinder and try to start it. But you really need to test that it is being atomised and  not too much raw fuel getting inside.

Fair enough. Sometimes there is a limit to how much to spend on anything. So what do you look at to buy? Another one the same or a proper Lister which maybe old but they do last if they were taken care of. I have a late 1950's CD 8hp that is as strong as the day it was made.

OOPS, not a good feeling. I would keep stripping it don during the day and searching for parts or replacement engine of a night. By knowing what is available and what cost is involved then an informaed decision can be made. Any luck contatcting a parts supplier?

Sorry I am unable to tell you if it is a sleeved engine or not so unless you have a workshop manual or parts book you will have to strip it down to find out. Maybe you can contact a parts dealer and ask to buy a sleeve for it and that will also give you an answer.
As for your anti-freeze freezing and cracking the sleeve/block I think there is something very wrong with the enti-freeze mix or it was not as claimed. Here in our climate we occassionally ned anti-freeze in certain areas during Winter but we have to be carefull when buying products for our cooling systems as not every thing is anti-freeze but is just a inhibitor more so for corrosion control than stopping the engine getting froze to death. If it is a sleeved engine hopefully it is just the slleeve and not the block. If the block is cracked then yes it is possible to repair it by veeing out the crack and making many passes with quality cast iron rods because in this case brazing it will not hold. This will take a lot of time and hours of manual labour and talent to do the weld properly. So would consider another engine replacement.
Question. If the engine is not under cover and out in the open why don't you run and exhaust that does not face upwards? Or why not build a roof over the engine?

Wish I could answer your questions on that. Spill timing is something I have only heard and read about but never had to do it. Maybe do a search here as it has been explained in th epast in simple terms with good outcomes.
Never tried to understand the internals of an injector, just free them up to make them work, sorry.
Soon enough someone with a lot more knowledge than I have will offer help. So get stuck into the fuel delivery system while a proper answer can be supplied.

It sure is as it is compression that heat the fuel air mix to ignite the diesel.

When cranking without using the decomp lever you do need to be serious about wanting to crank it over. Don't play with it mean to turn it over. Diesels rely on high compression to ignite the fuel air mix. If it was too easy to turn over compression it may not start. There is no shame when cranking to use the decomp levers when the weather or engine is cold or hot. It is just easier on you to start it up. Electric starts can do it without the use of a decomp lever when everything is in good working condition ie good battery and starter motor.