Curt
The best thing you could do is to get a camera and take some pictures. If nothing
else, buy a cheap throwaway, take some pictures, and mail them to someone who can
scan them in.
At that serial number, square butt vs round butt is not an issue. There is no
real price differential - particularly for a 6" gun.
If the rear sight is missing, then I assume there is a long rectangular cut in the
top of the frame, that held the adjustable rear sight leaf. I further assume that
it has a pined front sight blade, of some kind . Ie, not a forged front sight blade.
If it is a target revolver , and is missing the rear sight leaf, then my advice
to you is to forget it. You will have a lot of trouble finding a replacement leaf.
Later, Mike Priwer