Select-O-Speed. I would advise getting it running satisfactorily, and thoroughly operate the transmission. Though I would imagine trying out the higher gears/speeds might not be so easy, you can tell a lot from how it performs in the lower gears.
Be sure to check the fluid level and condition of this transmission and or look it over carefully, same as the rest of it.
There is a lot to know about these, I liked them, had a slightly newer model of the same tractor for years. With a loader on it, it may have seen more wear and abuse, check the front pivot pin/front axle assembly, you'll want to note any significant wear and or excess play in the assembly. Might be best to jack up the front end. Be safe doing that.
Find out what you can on it's history, why was it parked, when was it last in use, what problems did it have etc.