Guys-
Are the rivets aluminum, Monel, or stainless?
My "87 Cruiser has sheet metal type screws in it. Three on the helm side, three in the companion way, and three on the port side. It is also bonded across the entire 7 ft plus long flange area with 5200 or the equivalent. Hasn't ever cracked or moved any amount at all.
Might be a good idea to bond yours the same, and sink the new stainless or Monel rivets into holes stuffed with Marine Tex, JB Weld, or something else as solid. If the holes are badly enlarged, they should be filled in, drilled out, and even possibly sleeved with some sort of expandable metal sleeve with ribs if you can find such a critter.
You could also go up one size on the rivets, say from 3/16" to 1/4" if you have the source for the big guys and a tool for such large rivets. (Harbor Freight offers a two-handed rivet tool designed for auto body work that shoots up to 1/4" rivets for about $17.)
Joe.