I make the bottom booms 6" longer than the foot of the sail, and haul the sail clew with my patent rope outhaul. I usually use 2" x 2" knot-free pine.
The first photo below shows a BRE main and mizzen rig adapted for a Drascombe Drifter. Zoom in for details.
The second photo shows the rig on a BRE. In this photo the mizzen boom is made from a carbon mast leftover, so it is a bit shorter than 6".
(Please note that the mainsail in both photos is a reduced size "work" sail, fully adequate for west coast of Ireland conditions.)