Yes, you should be fine with the wheels of an '06 'Busa changing to an '08. What you have to look out for is the electronics - they are not interchangeable.
http://www.busaking.com
Assuming that we are talking about K series Gixer Thou. (K1 thru K7) Then YES they will fit. They are 1 inch longer and have more bracing. That means they weigh more too.
Assuming that we are talking about K series Gixer Thou. (K1 thru K7) Then YES they will fit. They are 1 inch longer and have more bracing. That means they weigh more too.