So, with the handy FasTrack chart, measure the gaps for a combination. 7/8" is not a track, so add 1 3/8" for 2". Not on the chart. Add 1 3/4" for 2 5/8". Add a 4 1/2" for 5 and 3/8". Add a 5" for 5 7/8". Bingo.
So, take out a 10" and use a 5", then use a combination for the 5 7/8" and the mainline is closed. You can also measure the gap at the preceding joint of the adjacent whole track plus the gap, which would have been 10 7/8". There's two combinations for that space.
Just remember to add a larger track to the gap, which means breaking a 10". This is what Rob was referring to about fitters.