Good question, I am going with the thought that the K frame cylinder has lot of space between the cylinders holes. Plus I don't think Bowen/Harton/ other gunsmiths would be doing it if it was not safe.
Now on the j frame, it has two problems, the 32 mag cylinder is not long enough, even if you bored it straight through, the bullet would be sticking out the front. S&W made the cylinder longer and stretched the frame to allow the 327 mag to fit in the model 632's.