Hi Jimmy,
I sand the butt with a 6" belt sander. It has a miter gauge and I made a vertical fence and attached it to the miter guide. It helps me keep the stock straight. The dowel inserts need to be trimmed off even with, or below the butt surface. If the butt is still curved, straghten it. Bending a pad to fit a curved butt looks like crap, the sign of an amateur job. The front surface of the pad may also be curved and that needs to be sanded flat, as well. My preference is Pachmayr Decelerator pads but that choice is yours. You will get better at it, the more jobs you do.
