I am in the process of mounting a 60" plasma above our fire place, I need to wall mount to be center of the fire place and mantel but the width of the mount is only 21" and there is a 2 x 4 dead center of the mantel. If I was to move the mount left or right so I could reach one of the other 2 x 4 it would make centering the TV on the wall mount 6.5" off center 3"-4" is max according to the manufacture specs.
8" off the top mantel is the header which means I can secure the bottom of the mount on the header and then only get one bolt in the center wall stud. The TV weighs 73 lbs and according to manufacture specs the mount needs to hold 4 times that amount so 292 lbs which means drywall anchors will not do the trick on the upper section of the mount. The mount I am using is a down and out mount which will bring the TV out 16.5" from the wall and the bring it down 27" from the top position of the TV, this is why the TV needs to be centered on the wall mount so it has a smooth transition from top position and the down position.
I have posted some photos of the wall in question and where the wall studs are and where the best position for the wall mount will be.
I actually thought about tearing down some of the drywall to add some support and then fixing the drywall. option #2 what if I take (2) 34" 3/4" x 2" secure those to the 3 wall studs but cutting out the drywall so as to have the cross member then center and secure the wall mount to the new cross members. Granted they will be visible when the TV is in the down position but will be hidden from view in the up position. By inserting the cross member into the wall it help reduce the distance from the wall, or should I use thicker piece of lumber.