Thanks guys for all the help. My 63 does have a square butt grip frame, so the grips fit perfectly. No looseness at all, and they fit my hands really well too. And the best part is I got them for $10 including shipping!
I wasn't sure at all about the box. I thought the letters SK might mean K-frame, but I wasn't sure.
The serial number on the gun dates it to the late 70's, so if the grips are about the same age that is really cool.
Thanks again for the info. I really like how much knowledge this group has and shares!