You simply need to measure the diameter of an easily accesable frost plug and order accordingly.
Also your auto parts may have cross referances in the suppliers catalogues as they can check by make/model as well as by engine model.
frost plugs already being used by cab heater. need a oilpan drain plug type heater. have seen these electric heaters advertised for other perkin engines. was wondering if it is available for a mf1433.