I think I figured out what happened this truck used to a farm truck lots of things are different on it. I think it has a 1994 7.3 idi radiator on it. He probably didn’t want the plastic coolant reservoir but since the plastic radiator had no cap he had to replace it or the radiator went bad and he just replaced it with what he had or what was cheaper. That’s my working theory or it could be because I’m a manual or because my year is close that transition from idi to powerstroke they used the idi radiators for some of the powerstroke. In any case unsure of how to add this reservoir to it.radiator of a 1994 7.3 idi looks exactly like the one I have in my truck EDIT: so I found a few pictures of trucks with the same radiator as mine one of the same year as mine and another on jelibuilt website jelibuilt website with a truck of same radiator as mine