I replaced my entire traveler track a couple years ago after one end snapped of while broad reaching in from the race course at Tradewinds.

First I had to drill out the remaining pop rivets, then I used the 10mm (?) box end wrench taped to the fat end of a long, stiff batten, and had my daughter hold it in place while I lined it up from above. We measured the placement of the nut by lying the batten on top of the beam first, to mark the batten with a sharpie, when the nut was approximately at the hole, make a sharpie line at the point where the end of the beam is against the batten, so then when you slide the batten inside the beam, you'll have a pretty close estimate of where the nut/hole should be, when the batten is inserted to the sharpie mark.

It took the two of us about 3 hours to do the entire track, about 12 (?) screws I think. And as mentioned above, start in the middle and work your way out to each end! Otherwise the new screws/nuts will be in your way.