This Model B, in addition to an aftermarket seat,
is fitted with the snap coupler equipment which Allis Chalmers
introduced in 1954. It appears that snap coupler parts intended
for use on other models have been adapted for installation on
the B. 
This shows the section of angle iron which holds the snap coupler's bottom latch. This is a nonstandard arrangemnent. The usual method of installing the snap coupler on a B was to turn the drawbar around to extend forward under the tractor and mount the latch on that. The hydraulic ram which extends forward to lift the arms mounted under the torque tube is not part of the snap coupler setup.
The lever between the brake pedals pulls the chain which opens the latch to unhook the implement.
This view from the rear shows the bottom latch which is attached under its mounting piece of angle iron. The bell around the latch guides the implement tongue into the latch where it snaps into place.
This rear view from above the drawbar shows how the mounting hardware is attached at the end and with a brace in front. The picture above this one shows the brace attached under the brake pedals.
Both lift arms are raised by the hydraulic ram at the right end of the lift arm shaft.
The left picture and this one show how the expanding hydraulic ram raises the lift arms.
Lift arm latch open.
Lift arm latch snapped shut.