i know with the drive off the housing it locks in foward when i move the shoe on the drive i dont remember if it locked in reverse
with the drive between your legs and the input shaft facing fwd the brass shoe will lock the prop CCW when it is in a straight line This is fwd gear.
When the shoe is turned fully CCW the prop will lock in a CW direction (rev)
This may sound just the opposite of what your thinking but the driveshaft turns the prop clockwise in fwd gear under power so it is locked against the shift dogs in the lower unit