Just took a quick look and found it where I figured it was. Even found a remnant of the pigtail. Wish all the stuff I go looking for turned up that easily.
Can't remember where I found this but it was attached to a smushed LH taillite assembly. It has the Ford oval stamped on it and a D3TB part number. Probably off a long flareside box as Ford didn't offer the short flareside between '72 and '76, when they redesigned it to match the wider rear axle. Basically all they did was shorten the regular 8' f/s box as it was already the proper width. If you can use it, Doug, you're welcome to it.
mike