Tonight was putting the radius on the board. No fancy concave sanding block here: just a flat block, a straight edge and a 12" fret press block to use as a radius gauge.
First I sanded at 80 grit and placed the gauge along the neck to look for light shining through the gap, and the same with the straight edge along the length of the fretboard in various spots across the width. Eventually when the gap got too small, I placed a small pile of dust on the fretboard then drew the gauge along the board a few times, leaving dust in the low spots. Once it didn't leave more than a trace of very fine dust I switched to 120 grit and gentle pressure