The model number is pretty irrelevant, you are as likely to have an 841 with a swapped hood or merely an emblem as 600 series with a swapped motor.
The diesel is solid, I pulled with one a lot of years, they will run far past where they should and can be kept operable very cheap. They also rest well and if you keep the bugs from turning the diesel can set just fine for a once a year bush hog job.
For giggles post all the numbers on the flat above the starter boss and that will clarify at least the trans age and what is was attached to originally.
Starter should be available somewhere local, have one on Craigslist from a part out in AL right now, set of brushes and bushings and a quiet evening and it is ready for the next 20 years.
Can’t see the shifter but likely a 4 speed, as a hobby farm toy it will be neat and a blast for you at local parades and such purtied up, but can offer some challenges missing a live pto, workable but not to easy for detail type work with driven implements.
Best thing to remember is the core of that tractor premise is just as simple as the original 8n, designed to be maintained with minimal knowledge, tools, time. These were kept working for decades by people without access to the internet!!!
There is no reason btw for the starter to be missing, that is my concern, often that means something was wrong and I don’t like unknowns. My suggestion matches an earlier one, I would drain the oil and refill with bout the cheapest I could find after I made certain the crank could be turned a full rotation, there is an access plate on the bottom that you can use to bar the engine over easier than fighting around the crank snout. If ok then I would drain the fuel put a few gallons of fresh in it and pull it off, sounds good then I would put the effort into the electrics.