As I seem to recall from my 1960's hotrodding days, the 3 speed "Hearse" shifter (It took transmissions to the graveyard)had a spring-loaded neutral gate. The Competition Plus 4 speed shifter didn't have that feature. I think I'd be prone to disable the reverse gate and use a 4 speed shifter, even if one leg of the 4 sped H pattern needed to be blocked off for my 3 speed Brownie.
I've got a 1961 ALF on a GMC pugnose chassis, with a 401 V6 and a 5 speed Clark transmission with 5th. gear direct drive. I'm planning to remove the fire bed and driveline mounted pump, and use an under/direct/over Brownie in place of the pump. The fire apparatus is too far gone to repair economically, so it will be getting a commercial 5th. wheel and a gooseneck trailer hitch, and become a heavy-duty trailer towing vehicle.
Jerry