Today I drilled and reamed the hole for the button, reamed the peg holes, and tacked on the fingerboard again.
To drill the button hole, I clamped the violin in the holder, which I then clamped to the workbench. With my left hand width as a guide against my work stool, I sighted along the top join line to drill the hole with a hand power drill. I then reamed to fit the button snuggly.
I similarly reamed the peg holes to fit the trial pegs. I measured them first to make sure that they were as thin and consistent as possible. I had to widen the right F hole just slightly to allow a sound post to pass through. Lastly, I tacked the fingerboard on again, hopefully a bit better aligned than last time.