My opinion (which may have little relationship to the facts):
The K frame .357 Magnum was fine with loads using the 158gr bullet (actually, probably any bullet between 140gr and 180gr). It ran into trouble with the lightweight bullets (110-125gr) moving so much faster than the heavier bullets. It's not unusual to read of people cracking the forcing cone on K frame revolvers using magnum loadings with the lightweight bullets.
In my M65 and M66, I shoot primarily .38 Special, saving the .357 Magnum loads for the M681, M686+, and M627. I wouldn't have any problem shooting the Magnum rounds in the K frames, I'd just make sure I limited them to 140gr bullets and above (after scrubbing the chambers thoroughly to get the .38 Special "ring" out).