Check out these rocker shafts (well not for mopar)

Bwahahaha! The main reason I won't switch to factory Magnum heads is the lack of shaft rockers! But, correct on all counts, Jesel, T&D, Harland Sharp, even Crane back in the day have offered shaft rockers for various makes of engines that originally had stud mounted rockers at one time or another...

You can switch all you want and have shaft mounted rockers. Hughes makes them.