No difference that I am aware of, except they switched over to the Nikasil cylinder coating, but that was quite a while ago. They have a rear-induction and a side-induction version, maybe one is better than the other, I don't own one. I had a 3W 78 twin in my H-9 Extra, it was a sled because I had one of the original Extras they built, weighed a ton. Plenty of power, but not so good when it quit once!! Most guys are using DA/3W 100's in those things now.