Flower car with a wooden floor? If there are 5 known to exist, where are the other 4? Show me pictures of the other 4 in any condition, and I might agree that it was a conversion package, but until then, I will believe that it is a one of a kind, built by a person that wanted to make a pick up out of a Plymouth coupe. Body builders in the 1950's wouldn't have a cowling around the back window, which is a design feature that came about in the mid to late 1990's with the Chevrolet pick ups... In fact, it might have even been a phenomena that is actually more recent than that date. Just not in the mood to do the research to put a definitive date on that fact.
Unfortunately, they have configured the Mecum website in such a way that I can't catch a picture of the car.