Reste;
Here is what I have on my 6" 686:
Understand, that is a picture of my 5" 625-6 but the mount base is the same. Here is where I got it:
http://www.cdnninvestments.com/sw.html
This is a stainless steel Weaver Style base. It is extremely well made, uses the sight cut out in the frame for a recoil lug and does NOT put recoil stress on the screws. On my 4" 625-8, I had to relieve the underneath of the mount (hidden) where there was slight interference with the front sight base - just a couple of light file strokes. This mount will handle any recoil you might run in to.
Here is another good choice:
http://www.jackweigand.com/swhpmnt.html
I prefer the stainless but there is really nothing wrong with a GOOD aluminum base.
Dale53