Some drums may fit outside the hub even though intended for inside, some may not. They need to fit snug on the hub and not have brake parts interfere with the hub.
Axle width will be wider with drums outside the hub, likely not an issue.
For a dual wheel truck the wheels are hub centered, installing drums where wheels go means no more hub pilot left for the wheels.
Single wheel trucks are stud centered, so OK to use pilot on hub for the drum and lugs still center the wheel .
I’ve considered it before but decided not to go that way, I’d keep drums where they were intended on the hub.
