I recently removed the very rivets of which you speak (there are lots of them).
HRL's method is what I used. The rivet heads are crowned and some are irregular, so I used a small angle grinder to make a flat spot which makes finding the center easier, then did what HRL recommends.
Carl

1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission