If you want to be correct for 18th c., or early 19th c., use iron/soft steel for the pins. As Necchi said, epoxy the grips on also. The epoxy makes a water seal, and helps to stop internal rusting. Make your grips oversized. Using a few tiny drops of super glue down the middle of the tang, glue one grip in place. Drill the pin holes in it. Then rap it on a piece of wood to knock it loose. Clean off the remaining super glue, and repeat with the other half. Now pin the halves together, and shape the front of the slabs together like you want them. Sand the very front faces of the grips as far as you want them. Then install on the tang with epoxy and unpeened pins. C clamps would give you the tightest fit. Clean the epoxy from the area on the blade forward of the grips with acetone, or white vinegar. Fully shape and sand when dry. Then, using a suitable punch, punch the pins out, one at a time, and slightly countersink the hole, and install a new pin that you will peen. Then apply the finish, and that's it. You can dress off the peened pins and touch up your sanding if necessary. Brass rivets/pins were not commonly used until later in the 19th c., so to be more correct, use iron. Nails, or drill rod, welding rod, whatever, but keep the pin diameter at no more than 1/8" if possible. Good luck with your project. Oh yeah. I think you would have much better luck working with wood, and it would also be more PC for slab handled blades.