At one time Eddietude had that part, don't know if it is still available.
that is the place where a diesel battery goes - pm Mike Warme for the right parts for the battery hold down.
The best Dodge that Dodge never made
Living the D-50 lifestyle since 1980
I've got the brackets and the bottom tray that it sits on as well as the removable bed piece for that battery. Let me know what you need. As for the hold down itself you'll have to make one. This was the norm for 84-85 diesels . I remove all the EGR crap from them and saw trays from gassers and weld in where they went on the 83's which is under the hood! This eliminates all that length battery cable. Pretty sure its a group 34 battery