[Model51]

I honestly don't know if the 51-815360-A2 drawing represents a part Ford put into production or not. Unfortunately the dates in the upper top right hand corner are not clear enough to read and I also don't have any of the Engineering Parts Release cards to know what this part was used for or when. The drawing shows a hardwood multi-piece design which is different than the "normal" one which is made from plywood. It's possible this design is intended for the rare instance of a Panel Truck with an 18 gallon tank. There's no cab wall behind it so it needed a different design seat. This is all just speculation on my part but this drawing just doesn't fit into my knowledge base very well.