If you are going to invest in a front end alignment I would recommend a 3 axle alignment, which my be what the folks who went to Prevost are referring to. This cost about $600, but is well worth the expense given the price for new Tires.

They place the bus up on 6 steel tables, use a laser device and then go through the entire process of aligning each axle. It is important to make sure that the steering wheel (correct position) is checked before completion, straight that is. and also test drive the bus before signing off on the alignment.