You will notice on the outsole of the boot that there is a shallow channel (it follows the contour of the lasting). However this is typically not enough clearance. Dremeling a notch in the outsole for the second wheel is an option and will not have a significant impact on boot integrity. I prefer using 3mm poly lifts on the front and 6mm in back. Typically this gives adequate clearance (under load as well) for the second wheel. The additional height in back helps match the Vapor boot profile, and reduces stress on the boots and rivets. Guys I do them for also like the slight forward lean it gives since the Hum'er chassis sits relatively flat. As far as alignment goes it's best to have a wheel on the front and back to center the chassis side to side. Front to back centering has some options. If you are just getting onto the Hum'er (or other all 80mm setup) chassis, many players notice its slightly difficult to "get over" the large 80mm wheel on the toe. In my humble opinion, many skate companies (that use all 80mm chassis) factory mount the chassis too far forward. I prefer to mount them a few millimeters back form center, this helps the players get over the front of the skate quicker and (I believe) allows for a more powerful stride.