Re: rigging question
Pics would help, but it sounds like you might be refering to rivets that hold the mast base that sleeves inside the mast section. If that is the case then the rivets should not be bearing any load. The rig tension should create enough compression to keep the mast firmly planted to the deck. If they sheared off it could be a result of ecessive rake or the mast leaning to leeward and trying to "slip off" the base which is presumably pinned to the deck at its pivot point.
Of course this is just speculation based on my experience with my last trailerable boat.
On my boat i drilled out the rivets, and then tapped the holes for machine screws. Through bolting is not necessary.
1979 Santana 30 Tall Rig