You need three (3) spacers for the rear wheel. Two of the spacers have a small lip on them which lip goes towards to wheel. The large spacer which goes between the Pulley and the frame is 1 5/8 plus the lip comes to 1 43/64; the smooth small one with no lip which goes between the brake bracket and the frame is 29/64 and the other small one which goes between the wheel and brake bracket is 7/16 and with the lip is 25/64 I don't know how the 2008 Mutt is set up, if its like the mastiff you will need what I described above. The Mastiff uses an 18 x 8.5 in the rear wheel with a 250 tire. The front is a 21 x 3.75 wheel, with two spacers both the same size 1 27/64 The front axle is a 3/4 inch axle. The rear axle is a 1 inch axle.
What kind of wheels are you planning on installing. I would make sure they are the same width as what is on the bike now, maybe you can use the same spacers and you won't have fitment issues especially with the rear tire rubbing on the belt.
Hope that helps
Carlos
