I have an 01 426. I have heard that the first two years for the 450 were basically punched out 426 motors to make them 450s. They were actually 439cc. I am interested to know if the 03 04 jugs will bolt up to the 01 426 cases and can I use my 426 head. I have six years worth of riding and probably 10 or 12 thousand miles if not more on it. It still runs good but I think it is time to go through it before it has major engine problems.