Mswlogo,
Do you NEED a block heater, NO, hold the glow plug for 10-15 secs and it will start as others have said. Will you like the way it sounds and acts when it starts, NO. Most of the engine wear is occurring in the 1st few seconds until the oil starts to do its thing. If the engine has sat for a few weeks without use, the oil has drained back and the pump has to do its thing even more.
I plug my heater in for 1 hour before starting and the engine is warm to the touch in an unheated shed. (I actually installed a 1 hour timer on the wire to the outside receptacle that I plug the extension cord into and yes it is 12 gauge cord, and just turn the knob and an hour latter I am good to go.) I also use synthetic oil too, I consider the oil and the block heater sleep insurance. My dealer said the same no need to install a block heater, BUT I did it anyway, it is my tractor I can do what I want with it and so can you