Jay Mott down here in Orlando was experimenting with building expediter trucks out of Pete 387's, but has pretty much given it up. He had difficulty getting Peterbilt to build extended chassis for him, then when they agreed to that they raised the price significantly. They didn't want to make any with single rear axles, and he was concerned that the price they wanted for the tandems was pushing the price of the truck way too high. Then the changes that he had to make to modify the chassis to handle the box were fairly intensive, also running up the cost. Last time I talked to him he was switching back to Freightliners for new builds.
Now, having said that, we checked out one of the Petes he built, and it was the first time my wife said "WOW!" in a factory cab/sleeper. It was great, for sure, but the price was climbing way out of reach for us as newbies.
Doug