A rod and spring would enable the barrel to move and return to battery, but nothing I have ever read about Johnsons, and none I have seen (and I have seen a bunch) had any arrangement except the sleeve (or shroud - I like that term better) with the spring built into the barrel lock in the stock.
I sure hope we can eventually see some good pics of that gun. I will also note that I have never seen or heard of any Johnsons being chrome or nickel plated. My feeling is that that rifle was originally a prototype, but someone (who???) worked it over to make a sporter.
I once said that sporterizing was taking a $1000 rifle, making a $200 rifle out of it, and paying $800 for the job. If I am right, this was a case of taking a $50,000 rifle and making a piece of cr*p out of it.