It depicts a chance meeting of two "different but the same" worlds, in more than one respect. Both the chopped top '56 Chevy Sedan Delivery, and the chopper sport the same style black/yellow flamed paintjobs, and both of their respective owners are giving the "thumbs up" to each other in mutual respect for the others work.
Powell is also sketchy about how long he owned the SD, only saying that he eventually sold the car to Boyd Coddington. Powell goes on to say it changed hands "a number of times" after Coddington, and that "...artist David Mann owned it for a while. He did a painting of it for Easyriders magazine".
Powell isn't real good on providing dates in this part of his book, probably owing to the fact that he couldn't recall them, or felt that they weren't really relevant in this section of his book. One can guess that David Mann owned it pretty close to the same time period that he did his centerfold painting, again, the painting was the centerfold in the Nov. '79 issue of Easyriders.
You'll also notice that in the Mann painting, the original chrome reversed wheels with the baby moons capped with a bullet are replaced with a set of Tru Spokes and spinners, and the lake pipes are gone. Whether Coddington, another owner, or Mann did these mods is anybody's guess.
I thought you'd like to know a little about the sedan delivery style of vehicles. Chevy (along with Ford, and Chrysler) offered the sedan delivery-style of vehicle for just about as long as they offered sedans and station wagons. The sedan delivery was your basic automotive (not truck) bare-bones sedan or wagon body and chassis, with the side windows replaced by a solid body panel, the rear seating deleted, and in lieu of a trunk lid (or in the case of a station wagon, its split liftgate/drop down tailgate), the body received a solid 1 pc. door with window, that was usually hinged to the L/H side, with the latch/door handle on the right.
In '55, when Chevy changed body styles, they came up with a feature that helped the delivery person's access to the rear of the vehicle, with Ford following suit in '57. Instead of hinging the rear door to the left, Chevy (and Ford) made the rear door to hinge from the top, supported in the open position by the same locking struts that the station wagons used on their upper liftgates. This allowed the driver even more access to load and unload the vehicles. They also offered a single bucket seat as standard vs. the bench seat, that allowed longer items to fit from the firewall to the tailgate on the R/H side of the interior. A R/H bucket seat was an option, and both seats hinged forward to access cargo behind them.
Chevy continued the Sedan Delivery line thru the '60 model year, when it was dropped, and it's niche in the light delivery market was filled in '61 by its replacement, the new Corvair Greenbriar van model, which itself was replaced in '64 by the "first generation" G-10 1/2 series of delivery vans.
Here's a tip on ID'ing a real GM-built sedan delivery. There are quite a few station wagons out there that have had the side windows filled, and the SD's tailgate added to it (the recesses for the top hinges are stamped into every wagon tailgate surround). It's an easy conversion, but if you look at the VIN ID tag (not the cowl tag on the firewall) on the left door pillar, you'll see a code similar to this:
Here's an ancient photo (only one I can find) of the '57 Chevy sedan delivery I owned, taken around '79 or so. Originally when I got it, it was painted that ugly Chevy "Surf Green", and had the original New Blue Flame 123 6, and "three on a tree" transmission. I replaced that with a SB 327/Powerglide combo shortly after. I drove it around like that for about two years, and then I came across a deal on a BB 454/TH 400 combo from a wrecked '70 SS Chevelle, and an all chrome '58 Olds rear end with 4:11 gears to go with it.
It was raggedy, the interior was loud and smelled like old gear oil, and that fucker would MOVE when you mashed the loud pedal. I loved it! I finished up the bodywork on it - including an all-steel tilt front end I did (that could be raised and lowered via two convertible top rams with a flip of a switch on the dash) , but never got it past the primer stage in the 6 years I owned it. As is the case, somebody made me "an offer I couldn't refuse...." on it, for a trade of a '64 Pan and cash for it. I wish I still had that sedan delivery today. Oh, and the Pan, too!