I have probably put in 10 million pop rivets, and there is nothing to it. If you use 3/16 rivets, use a 3/16 drill bit. Your comp-tip is about 1/4" thick, so you need to purchase stainless steel rivets with a .375 grip range. If you do not have a comp-tip, use rivets with a .250 grip range. You can purchase a rivet gun at any hardware store, and probably even at Wal-Mart. A rivet gun will run in the $20 to $30 price range. Not all hardware stores carry stainless rivets, but most stores can order them.
Just line the rod up on your mast with the mounting fixtures in place over it, and drill one hole at a time. After you drill the first hole, go ahead and insert the rivet and pop it. then drill the other hole through the mounting fixture...can't miss that way.
David