I'm not sure about one of one. There's at least two more out there that people have built. I've seen them at 2 different POCI conventions.

There's one that is maroon that has nicer styling in my opinion. Not sure if I can find pictures of it.

I think you would dong your noggin every time time you tried to get in that orange one. Needs the back screen cut back like the other

Here are some pics to illustrate the difference.  The 4-door hardtop has the large wrap-around rear glass, shorter doors, and no window frames since it is a hardtop.

 

The El Camino has longer (2-door length) doors, shorter roof overhang, and was designed as a "truck" (well, actually kind of a 2-door wagon with the rear roof cut off...), and thus better proportions and functionality.

To me,back windshield looks like the front. If you look at it close..looks like a car with a very long snout(front end). Just odd looking.

The 59 and 60 El Caminos were built off a 2 door 6 passenger wagon chassis, including the rear flank gas fill door and a "banana" gas tank. The banana gas tank was due to the wagon having the spare tire under the floor where a gas tank would be in a car, the tank fit around the tire.

The Pontiacs, including the white 59, have a car gas tank, filled from the rear, so all were likely made up from a passenger car. That maroon 60 looks very well done using the El Camino roof, but it looks like the tail gate does not open? Hard to tell from the pic but is that a gas fill cover above the plate? The El Camino used the rear wagon gate, just covered where the glass would be and had a Blank where the exterior window crank handle was. It unlatched via the same interior latch/door handle that was on the wagon.