S&W Model 350 as a GNR platform

Or something strange/different. Supermag cals, 445, 414, 357 max. Or stay with the rugers for the supermag cals

would fit in the cylinder window.

It sounds like a great idea but in practice can be problematic. I have had some .45 ACP moon clipped revolvers and they always work great. But that's low pressure and short case rounds. Ditto .40 S&W and even 10mm. But as you get longer rounds the wobble factor gets you. Things don't go as smooth. You have to fiddle with them, they can bend the little clips.

Also at higher pressures the whole works can lock it up tight. I once shot some slick aluminum CCI snakeshot rounds in a S&W M625 and boy was that a mistake. It locked the gun up instantly. The aluminum does not grip the chamber walls and is jetted against the recoil shield, then it expands! Not good. The rim in a wonderful feature for the DA. ON a SA you can do rimless provided recoil is not sufficient to make bullet pull a problem with the rounds that headspace on the case mouth. It probably shouldn't work as well as it does but a SA with rimless rounds have been fun for me. Gary has made some in .40 for me that are great. Ruger's in .45 and 9mm work amazingly well too. But for the DA, stick to short, lower pressure rounds and you will be happy.