Can't say this for sure, but many Jap tractors have a rubber hose (about 5/16 or 3/8 inch) at the bottom of the radiator leading to a tee and a drain type fitting. The other side of the tee has a hose going to the engine block with a hose barb fitting at the bottom of the block's water jacket. Opening the fitting or removing a plug will drain both block and radiator.