I have an older 686 with a 6" barrel that I think I bought in 1987. I have ordered a Weigan scope mount and looking at some information it says that I would probably have to have a third hole drilled and tapped for it. When I have the cylinder out to the side it says to look to see how many holes you have in the top side of the frame when you have the firearm flipped upside down. I have no holes coming through the top of the frame but I assume there are two holes because there are currently two screws holding in the rear site that is presently there.

For a small light weight red dot do you really need three holes to hold the scope mount on? If the mount does not come with new longer screws where would I find the screws to hold the new mount in place and what size am I looking for?

Thanks