I recently came across this photo of a FJ panelvan with barn style doors. If you look closely on the second photo you can see on the inside of the doors bolt holes where the top part was originally bolted, and the bottom part has the recesses for the hinges. So basically its the top and bottom tailgate welded together and then cut in half.
ourtouringpast.com THE vintage caravan restoration website
and home of The National Caravan Museum.