Following Matt Miller's excellent guide, I was able to replace my broken mast step with a new one in about 45 minutes.
The tools and replacement parts (mast step with proper rivets);

First step, drill out the old one (remove head and punch out the remaining cylinder);

Basically use 1/4" drill bit and drill out the rivet heads, use punch or similar to knock the cylinder through.
Once I did that, it literally popped up above the bar like this;

Now I simply unscrewed the old mast head and screwed in the new one - use care as you need to make sure you are not too high into the mast base. These new ones the hole goes all the way through, and according to Matt you need to make sure it's a smidge below or you'll run into problems with your bearings wearing out etc. To get it seated, I tried the clamping trick, then went to the jack on the dolphin bar area, then in addition I had to rasp file the aft side and I used a rubber mallet and a ratchet extension to smack it down (not hitting the casting at all, just the bar in the middle bottom of the casting. Here I am with the jack in place, one of the clamps and putting in my first rivet;

The one thing I didn't realize about rivets is you push it up tight to the rivet and clamp the handles together, release and shove forward and clamp again, and then it usually snaps off at that point. I had to do it up to 4 times to get it to go on some of them. Finally done (don't mind the orange paint on it - that was from the clamps);

Once complete the key thing is to go back and tighten up the dolphin striker nuts on the the two ends of the boat under the corner castings. I should also mention, it's a good idea to loosen those prior to clamping things down as it makes it easier to do.
Not the best how-to in the world but really just gives a flavor for what is involved. See Matt's document here;
http://static.hobiecat.com/2010_archive ... eplace.pdfThanks Matt for creating that guide!!
-Lyle