I'm not sure the forcing cone thing is an issue anymore with the newer guns.
Newer, better, steel?
A redesigned barrel socket that allows a thicker walled barrel extension. I don't know the dimensions compared to the L frame, but if was a betting man I'd think if Smith would go to the trouble of a redesign, I'd bet the L dimension would be something to shoot for.
It's not the barrel socket
If you look at an old K frame, you’ll see the bottom of the barrel is shaved off at the forcing cone. Whereas the new ones do not have the barrel shaved off at the bottom. The barrel shank is full thickness on the new ones, and shaved on the older ones.
That flat exists to make room for the gas seal on the crane/cylinder. Really, the real work was done on the crane & gas seal to allow for more room for more barrel thickness at the forcing cone.
