Putting a tank heater on one ninety

Just wanted to report back that I did find the rear frost plug.  You can see the top half of plug in the picture.  It is nearly at the end of the engine above the starter, but there is an oil line and other things in the way.  I suppose a punch could be used without deinstalling the oil line and hydraulic lines to remove the plug. 

There isn't a lot of room between the engine block and that oil line for the heater though.  The pig tail cord may be a challenge but since others have done it, it must be possible.  For now I am going to install the circulating tank heater and come back to this problem in the spring when I take the stack and hood off. 

Allis sure made it a lot easier in the later models to install the engine heaters versus this earlier model.  Thanks for all of the help to those that responded.

To explain the peculiar looking bolt at the top, it's custom made by me. The intake manifold is in the way to where a bolt won't go in. We had to cut off about an inch long threaded part of a bolt and cut the screwdriver slot into it. We then started the nut onto the homemade bolt, then threaded the stud into the threaded hole in the block. After getting the stud bolt threaded into the block by about five threads, we tightened the nut up with a wrench. darrel