IH with BD154 engine block heater

[IH3444]

Has anyone installed a block heater into the BD154 engine? Mine starts when cold, about 20 degrees F, but I would like to install a block heater. I have a lower radiator hose heater, and if I can't install a block heater, I will use the lower radiator hose heater. I have looked over the engine block, and haven't been able to find a freeze plug to remove and install a block heater. The engine is a 1971 era vintage. Thanks, IH3444