I string the center line on the boo and cut that pattern out.
I then sand to the line and then taper the boo from 1/8th at the riser to 1/16th at the tips.
Before glue up, I lay all 3 pieces together and string end to end again to get it straight. Then I drill 2 holes in the riser section where the leather grip will cover them later, and drill a hole on each side of the tips for toothpicks to hold things straight when gluing up.