Me too, I've replaced countless rivets on the tramp, mast, etc (H16 86). I just drill 'em out and put the largest ones in a can. The mast and boom aluminum thickness isn't much - about 3/16" you figure?
Tip of the Day (plag from Murray's catalogue) - when I tried to replace the rivets in the main sheet track, the rivet gun wouldn't fit into the track to seat the rivet properly. Murray's catalogue suggested, and it works, to slide a "stop sleave" over the rivet to extend the reach. The stop sleave is the round stopper on your trap line that holds the handle in place and keeps it from sliding down. It's Nico pressed to hold it in place. Anyway, you need to buy a couple and keep them in your sailing tackle box. You slide this onto your rivet, then put the rivet in the gun and it allows you to fit nicely into the sheet tracks to rivet your rivet.
PS Is there any better on-the-john or bathrub reading better than a Harken and Murray's catelogue? Is there?