I have leather faced quite a few pads, and pretty much all of my own guns have a leather faced pad. I mostly use pigskin, but any thin leather should work; I don't think it has to be super thin, my pig is about probably .025 - .030 or so. You need to sand off any markings on the pad and I think you need to round slightly the edges of the pad, so there is no proud edge to catch. Sanding , or wiping to get the mold release off gives good adhesion. I just use Barge and apply it liberally to both pad face and the oversize leather, soak it in well, kind of saturating the leather, let it dry a bit and apply it, pound around the leather with your leather mallet. When dry use a sharp! exactor knife or such to carefully cut the leather around the pad, keeping the knife pretty much parallel to the side of the pad. You can use 120 grit sharp paper to carefully sand the edge, and If you have stained your leather, you need to re-stain the cut edges, You can use an acrylic finish (Tandy's) if you wish or just finish like you shine your shoes. Maintenance is more shoe polish. I have never had one of my own come loose, and don't hesitate to put the gun in a snow covered gunrack. Works just as well as fully leather covered, but much less work, but lacking the "cool" factor, of course.
Some good-looking pads shown here.