To make lead rivets, I drill a hole the size of the hole I want to plug in a piece of metal about the same thickness, then take a tapered reamer I got from the local hardware store and ream out the hole to a taper but not so deep it comes out the back side. The hole should be straight with a taper at the top. Then cut off a piece of a tire weight or soft copper grounding wire. Pound the lead or copper into your tapered hole till you know its full. They push out from the back side pretty easy, now just put it into the hole you want to plug and hammer it it. If you really want to make nice rivets, use a piece of flat stock with half a hole to form the head of the rivet with as you hammer it into shape. I filled plenty of carburetor holes with this method with no leaks. Making the half of a hole in the flat stock was the hardest part!
