I believe that you will have to remove a "freeze plug" and then press the fitting into the block. Take a look at the attached video. It may not reference your particular tractor but I believe that it will show you what has to be done.
Well maybe "not so fast". I couldn't find a picture of the part you specified either. What model tractor are you working with?
Good morning DustyRusty. I did get that far, but the OP's question is still left unanswered. The OP is going to have to let us know what model number they are installing the heater in. As far as I can see, there are no pictures of the part on the web.