Patching Baffling, 3/32 C-Sunk Rivets, 1100 Aluminum?

Old baffles need upkeep in this neck of the woods. I was going to try my
hand at countersinking 3/32 rivets and hereby ask advice what is the best
way to press in the dimple, best tool too and where to buy it. Because on
the cylinder side of the baffle, like the opposite side of a plate nut, you
don't want anything protruding.

Also isn't baffling pure aluminum? Or something like 3003 or 5052? I was
thinking of using something soft because of the tendency for cracking.

Thanks.