I had a similar problem with my '92 legend. I didn't want to remove the floor, so I tried self-sealing pop rivets. They worked like a charm. I drilled out the old rivets and replaced with the self-sealing rivets - I used some marine-grade sealant around the shank of the rivet before installing. I've had my boat in the water for a month now and it isn't taking on any water. It honestly took about 15 minutes per rivet - the most difficult/time consuming part was drilling out the old rivet. You'll need a pretty heavy duty rivet gun (which I was able to borrow) and the rivets. It cost me $25 for the rivets (they only sell packs of 100) and about $20 for the sealant.
I'd be happy to provide more detail if you are interested.