Sorry for the late reply, but this site's format only accepts one of my PCs that I rarely use.
(Even then, I cannot type in a reply; I must cut'n'paste from Notepad!)
As Kyle noted you will want to ream the holes and custom-cut rivets for a press fit.
This will allow them to only require a simple "uspet" of the exposed portion, rather than ugly peening.
Knucks are brittle, and prone to splitting, so setting the new rivet demands care.
I use anvils with a ramp cut into them to push the rivet outward, as shown a http://virtualindian.org/11techleaktest.html
The easiest way I have found is to hold the anvil in a vise, slip the head over it and then twist to hold the rivet's head firmly, and then smack the exposed end with a hammer in my free hand.
The most difficult aspect to seal is between the shoulder of the nipple, and the thin raised lip upon the casting.
If this lip is blemished, it might be dressable; If it is damaged, it must be repaired.