Dave,
The legal climate for importing tractors with non EPA compliant engines seems to be undergoing a major change. To the best of my knowledge, CBP sells crate tractors FOB China which means you pay in advance and import the tractor yourself (with CBP's help, using their customs brokers, etc) bottom line is you are the importer.
Have you shopped any US based dealers to see if the tractor you are looking for might already be in the USA? This market is very competitive and you may be surprised at how little more you would have to pay for an assembled and tested tractor than for the self import crate tractor and you avoid the possiblilty of losing the tractor to customs and even possible fines if the paperwork is not correct. You may even get some warranty service and parts support!
If you decide to import anyway, be aware that customs is actively looking for and inspecting blue tractors because of legal action NH took agianst one chinese company who paid NH the ultimate compliment by imitating their styling. As I understand it, proof it is not a NH look alike is up to you, hard to do when it is in a crate. Customs agents are not Chinese tractor experts and one blue tractor from China pretty well looks like another.
I have heard rumors of tractors being "turned around" and ordered shipped back to CHina or destroyed but I do not have any first hand knowledge of this, perhaps CBP may know more about this aspect.
I am not trying to discourage you, if you are comfortable with the transaction knowing these things than go for it. My intent is that these things not be a surprise if you should face them for the first time AFTER you pay your money. Best of luck!