Case 580CK Block heater

I have a 66-67 580 CK Diesel without a block heater and 1 is needed. I have found 1 that is 5/8 thread, but where does it mount? The only threaded ports that I find are on the left a 1/4 or 3/8 drain petcock and a 5/8 on the right rear that has the gauge mount. I also see no soft-plugs for a soft-plug mounting.

Case 580CK Block heater