ib2v4u pretty much has it. Fit the scales as well as possible before mounting. File the pins/rivets as close as you can, and sand everything flush with a hard backing block after final assembly.
I prefer using Corby bolts, as they hold the mammoth down just snug enough. You won't have nearly as much problem with the mammoth moving or warping later on. With mammoth, plain rivets can pull loose. Brass and nickel work well with mammoth. Avoid stainless rivets/pins/bolts......they can get too hot in sanding and scorch the mammoth easily.
Give the whole handle a light hand sanding up to 2500 grit and buff LIGHTLY....avoid heat at all costs with mammoth. I prefer the 3M polishing papers ( the color coded cloth-like ones) which go from 400 to 8000 grit in a package. They will leave the mammoth shining and smooth. A touch up is quick and easy if needed with them, so I usually give a half sheet of each in a plastic bag with a special mammoth handled knife as a maintenance kit.
DO NOT PUT OIL and finishes on mammoth. Thin CA works for filling cracks and voids. There is a kit called paleo-bond that is made for restoring and filling things like mammoth. It is worth it if you have a tusk in need of major repair, but plain thin and medium CA will work just as well for most handle grade mammoth pieces.
I pre-shape the scales until they are almost the desired size, and flatten the backs. I then set the scales on waxed paper and flood all sides with thin CA. Let it soak in and cure for a few days. Re-flatten the back, and finish shaping the scales. They will be stable and polish better with this treatment. Any cracks or splits can be filled the same way, just keep repeating the CA treatment in that area until they don't show up any more and are flush.
