Reply to Jimmy977:
Ok Neil, this D4 I purchased is very complete. The air cleaner was off when I bought it so I really noticed the hole in dash. If there was a cover originally, I think it is the only part missing from this machine. Thanks.
If your dozer was equipped to have a cover plate for the mag hole in the dash, there would be a slot above the hole, and a bolt hole with a nut below the square access hole.
The cover plate was available for at least some of the J model D2s but I don't see any of the other tractors equipped to accept the cover.
I do have one on one of my D2 Js, they are a pain to put on and of no real use, and on the U models might be impossible to put on or remove without pulling the air cleaner and would not be removable with the crossover pipes for the dozer in place.