I agree with Terry concerning the models. I have restored  an OC4 crawler, a HG crawler,a 66 and a 550. The crawlers were very expensive however the 550 had low hours and was in excellent mechanical condition. The 66 was in fair condition but was relatively easy to repair and the parts are readily available at reasonable prices. The 440 would be a great tractor to restore but you will have to pay a premium to get one.