I don't cast, so I can't help you with the first one. I can tell you reaming to Max didn't change accuracy with .38s and mags in mine. My shortie Maxi wears an Allen 9 round butt stock cartridge holder. That contains 3 of each, maxi, mag and .38. It's my go to farm/truck gun.
The SB1 frame is not a no no. You can use it as long as you don't go wild. I have all my centerfire rifles on SB2 frames.
I swapped frames, and swapped frames, and now I have one spare SB2 and 11 rifles, and none need tinkering.
No, they don't make a .357 SB2.
I'd add the .30-30, but if you've got the .45-70, do you really need a .444? But, if you've got the time and bucks, why not?
Pete