Re: ok this isnt normal
does it have lots of vibes at the top speed of 30mph?
If so crank being poorly trued and seriously out of balance could be the problem as has been mentioned but also since you say you shaved head down piston hitting head could also be an issue if head was shaved down to far for being used with one head gasket as has also been mentioned.
My question is, have you run this engine combo in the past before the main bearing change?
if so did it have a top speed higher than what it currently has?
I dont always ride WOT, but when I do..I do my best to keep the rubber side down..Ride safely my friends!