Thanks for responding. The best clue to the frame size of the .357 Bisley Vaquero Jimbo357mag posted a link to is its 45 ounce cataloged weight. That indicates a full size BH frame, so it looks like the answer to my title question is “no.” Maybe Ruger will get around to making a Bisley newer Flat Top frame .357 after they fill their back log of orders. The idea looks like a logical modern SA to me. Add a .38 Super extra cylinder and a few reloaders who have shifter away from SAs into modern matches just might buy one, plus there‘s always collectors that will add the odd balls to their collection. My BH .357 has a distinctly heavy fell to it. That’s great me target shooting but is undesirable for woods carry and many target shooter prefer lighter handguns. With or without a convertible cylinder I think lighter .357s would appeal to a lot of shooters.
Edit to add: I see this 100th post promoted me to "Single-Sixer" which is a gun I've never owned. I wonder how many posts it would take to to be labeled as the owner of my .480 SRH, a "SRHer"?