Welcome to TBN!
There is actually a fairly long thread that just started on whether you should periodically start machines that sit for extended periods of time....let's just say it's a contentious issue. Folks posting in that thread described situations where they had machines sit for even ten years, and all they did was put a fresh batter in it, prime the fuel system (I think) and start it with no problems.
I bought a very old dozer from my neighbor, and it sat for two years....we put a battery in it, and it started right up.
Some folks will likely suggest any number of things like pulling the injectors or glow plugs and squirting some penetrating oil into the cylinders and let it sit for a couple of days, then letting it crank a bit with no compression to get the oil moving. You could actually change the oil and filter before doing that so you're moving good oil.
Some folks will leave the injectors/glow plugs in place, but spray WD-40 into the intake to try adding a little lubrication while it's first cranking (probably need a helper).
Other might suggest pulling the compression release or disconnecting the injector pump (many have an electric shutoff tied to an oil pressure sensor) then cranking the engine to get oil pressure up before actually starting it without trying to get anything into the cylinders first.
I'm not familiar with Long tractors, but I think I'd either use the compression release or figure out how to disable the injector pump (electrical wire, or loosen the fuel input line) so the engine can't start, then crank it for a bit (maybe 15 seconds), then try to actually start it. I'd look at the oil first, and if it looks milky, or like tar, I'd probably change the oil and filter first, just to be safe.
Let us know how it works out!