Allis Chalmer's G maintenance question

We grow about 12 acres of vegetables here in the Hudson Valley of NY. We use 2 Allis Chalmer's "G" tractors for all our seeding and cultivation. They are used every day. We couldn't farm without them.

In the three years I've had the first one, I'm embarassed to say that I have NEVER done any non-engine-related maintenance to the tractor. I am completely comfortable with everything I need to do engine-wise (that's another story) but I have NO IDEA what I should be doing to keep the REST of the tractor running smoothly for another 50 years.

The new growing season is upon us and I know if I don't do it now, it'll just get put off until fall again, and I really can't let these tractors break down!

I have been changing the transmission oil in the main body of the tractor... that was obvious, but.. .there are square-headed bolts on the rear axle... anything I should do with those? Do I need to repack bearings? What other things should I be doing?

Any help would be REALLY appreciated,
-Ron
New Paltz, NY

Actually, I have no problem with the maintaining the ENGINE... it's the NON-ENGINE parts that I need help with! Like... Am I missing grease-points? And what are the square nuts on the back axle leading to?

Thank again!
Ron