I attended the Golden West Chevelle & El Camino Appreciation 2010 day in Glendora, CA on Sunday, and the President's Trophy for the show was awarded to the owner of this extraordinary 1965 four-door El Camino, a very clean conversion indeed.
As near as I can work out, the guy started with a four-door Chevelle sedan and lengthened the frame to swap in the El Camino bed instead of the rear deck and trunk. The rear exterior panels are El Camino, but the inside of the bed is all custom, with a hardwood floor.
Usually custom jobs like this are real Frankensteins, but this car was clean as hell. Very well thought out and executed, inside and out. It also featured a late model EFI truck motor:
Those stupid-looking big wheels sort of ruin it for me, though.