Scottie: With regard to the tuneup question, changing oil/filter/plug(s) covers most of the bases. As far as tuneup specifications go (plug type/gap, oil type and capacity etc) that depends on the make and model of the engine itself, best bet would probably be to try and track down that info through a dealer/repair shop or possibly the engine manufacturer's web site.
On the subject of the tractor, I would stay away from making any major modifications. Replace what's "broke" or "don't work" and leave the rest alone. The speed (or lack thereof) is a function of the gearing in the transmission and will require MAJOR SURGERY to alter, again best bet is to live with what you got!
Hope this helps a bit, without more specific info it's hard to answer the questions except in general terms.
'75 GMC "Blood, Sweat & Gear$"