Jim, I have made a few flat belts & have been to a few leather shops that join leather belts, they have a tool that is adjustable & can strip half of the thickness away , I just do that to both sides, I have also used my 1" belt sander to thin the belt to about half thickness, then I join with "Barge" all purpose cement (suggested by the leather shop) also make sure your belt is "set" dead straight, using a long ruler as this will obviously effect alignment, compress with a clamp (block of wood works well with wax paper above & below the joint) & let set for 24 hrs, & as Daniel has said re; camber "just enough so that you can actually see the crown" is all that is needed on the camber.