I'm in the process of converting a 1989 Trek 8500 mountain bike frame to ride on 700c wheels with dual pivot caliper brakes. The frame has 6mm bolt mounts on both the front and rear but they have different reach lengths. The front is 51mm and the rear 59mm. Ideally I would like them to match, does anyone know why they don't? The dropouts are resting on the axle.

Second, does anyone know of an affordable brake set with a reach range that covers both the front and rear of my frame. I would like the brakes to match and I don't want to use the brakes with 55-70+ range.

Third, what do you think about filing the rear drop out to decrease the rear reach to a more common 57mm?

Thanks.