US is federal state. Not exactly homogeneous, but still, at least you speak the same language, have the same currency.
Meantime EU is gang of (very) different tribes. But rule is - there can't be any obstacles for random citizens to use junk which is legal in any other EU state. And here starts funny part
I don't know about tractors, but for vintage cars, there is very liberal regulations in few countries, like Lithuania. Or for motorcycles in Belgium. So there is an option - if person really wants to have his transport, he can "legalize" or lets say - "cross EU border" in one state and then use his metal free in any other EU member state.
If you are north FR, where BE-NE-LUX are, there should be a lot of holes for your tractor. But that should be studied.
Sad thing for you is that GB is no more in EU. There were flying trough customs very creepy stories
If I were you I would look how can I sell Kubota and what they want for one in FR. If the gap is big, I would just bring existing one and just use it. Chance that someone will ask you anything is near 0. If you dont drive on roads.