I don't think the K-frame was ever lengthened to get a longer cylinder window. I think they just shortened the rear end of the .357 barrel at the forcing cone to accommodate a longer cylinder. The .357 is only about a tenth of an inch longer than a .38 ctg.
The J-frame WAS lengthened to take .357 ammo. But they needed to beef up the gun a little. I still think it's too small for a .357. The Ruger SP-101 is the smallest .357 I own, or want.
I never owned a Model 10, but had the stainless variant, Model 64, a heavy four-inch barrel. It shot extremely well and had a fine balance for point shooting. I used Pachmayr grips on it. I traded up to a M-66-3 .357, used with the same grips. It's my single favorite handgun of all time. But I don't run many .357 rounds through it. I carry those when warranted, but shoot most .357 stuff in a Ruger GP-100. Even it doesn't get full .357 ammo a lot. That's for killing things better, not for routine range ammo.