Hi All
I don't know a lot about the monel v stainless rivets, but I'm sure that the monel rivets are strong enough, its what Goodalls use and recommend, and they are a hell of lot easier to drill out, if need be, more drill bit friendly.
I worked casually at the fibreglass factory when I was younger, and they used rivets there when making water tanks, when they popped they split out into 4 sections and set like a anchor, I don't know if something like that could work with carbon masts, they were stainless steel.
Regards