There are three screws that secure the side plate to the frame. In @WyldeDime pic in post #8 you see two of them, the third being covered by the grip. The screw covered by the grip looks different than the other two in that it has a flat head as opposed to the convex head the other two have. If the screw directly under the cylinder has a flat head it is definitely the wrong one and you will need to try swapping it out with the other two convex head screws and checking fit of the cylinder. If the screw under the cylinder is already a convex head, then simply swap out the other convex screw and check fit. If neither convex head makes a difference then I would contact S&W and arrange to have the revolver sent in for repair.
The frame lug can be replaced by the do it yourself skilled man, check out this thread for a detailed guide, once you source a place to obtain the replacement lug.
http://smith-wessonforum.com/s-w-smithing/125996-frame-lug.html
You can find a replacement frame lug here…
https://www.gunpartscorp.com/search#query=686 frame lug
The frame lug can be replaced by the do it yourself skilled man, check out this thread for a detailed guide, once you source a place to obtain the replacement lug.
http://smith-wessonforum.com/s-w-smithing/125996-frame-lug.html
You can find a replacement frame lug here…
https://www.gunpartscorp.com/search#query=686 frame lug