I'd use a 22 mm FET+1 driver, shaved down a little. Driver is wayyy easier to mod than I thought - 4 wires: LED+, LED-, switch, and grnd to switch. Clearance is tight - no room to piggyback anything in there. Driver was glued - used a solder pick thru a LED wire hole to break the glue seal - easy by hand. The switch is a true side mounted PCB, no switch LED.