Acoustic Guitar Construction

I suppose if you are compensating at the nut end some sort of power cut off saw would be useful -- I generally just use my fret saw in the miter box to trim the ends of the FB.

Looks like you've already accomplished the task, but...
What about getting the cut reasonably close with a handsaw/bandsaw, and then putting the fretboard on a rectangular carrier so the centerline is perpendicular to the short edge, and then sanding with your Lee Valley shooting sander? Planing should work too, if you back up the far edge to eliminate tear-out.

Another good idea, thanks.
Getting things perfectly straight, perpendicular, flat - I'm challenged in that arena.

Already been said, use a miter box and hand saw

ditto