if you take a metal tape measure, hook the end in the track in the top of the beam. Pull it forward and bend it around the front curve of the beam. The centerline of the rivets is right on 2". You might want to add slightly and go 2 1/8" to 2 3/16" because if this traveler is left up when stepping the mast, the mast base can catch on it. Other than that the trimming position is pretty good there.

I did see one F18 pull two screws out of the backing plate...they do a poor job tapping those and I kinda wonder if they don't just run the screws in a regular hole and forgoe the whole tapping process.