Don't drill right through and bolt to the other side of the beam as it will compress and may eventually crack at the bolt holes unless you put a spacer inside the beam for every bolt. I've replaced all the rivets on a few boats now. I used 12 mm ali tube as it is more stable than a batten, then attached some flat to the end that can be bent, to this I taped my spanner. I used a light dust of spray on adhesive on the locking nuts to stick the washers on enough to get them on the bolt. To hold the nut in the spanner I used some tape stuck to the spanner with the sticky side up so that it lightly grips the nut. Start from the middle and work your way out so you can see what your doing. Once you've done the first couple it gets very easy so you may as well do them all while your there. The nut's lock in because of the shape of the beam so it's easy to retighten if needed at a later date but I've never had to.

I give everything a smear of duralac as I put it together so that it doesn't start corroding straight away. When you take the traveller track off, the holes will have pulled up I don't tap them down, the bolts pull everything flush as long as I use the exact screwdriver for the head