What you've bought is a tractor from the early '70s up to the late '80s. Depending on the hood decal, it could represent a 4430, 4440 or 4450 tractor. I have scanned a page or two out of a collector guidebook that shows the differences and I could e-mail it to you if you wish.
Value? Depends on condition, but one that is rebuildable is maybe around $120, and one that is "excellent" or repainted would be in the $250 range.