4-Door with 340 from the factory?

So what exactly is the fender tag code that specifically called-out the closed-chamber Slanty head from the Assburn/Rollvarry You now posses?? Or does it not really exist??
According to Doug Dutra, they were a prototype head. I think he said there were like five made. And of course, he has one, too. lol Being a prototype, I'm not sure there'd ever have been any code given to them. He said the one I found should never have made it on a production vehicle, but they pulled it of an Aspen. At least that was the story.