Mounting a 60 inch TV where studs are 22inches apart. Can I use 2 steel plates that are each 48 x 1 1/4 x 1/8 inch thick and then bolt them to my bracket and to the wall studs at each end and one in the middle? Will that give me enough strength and support over dry wall?
Personally I think you would be far better off mounting a sheet of good quality 3/4" plywood between the studs. Size the plywood so it a bit larger than the TV mount plus the extra amount so that it extends to the studs on each side. This will provide a far superior mount than that thin steel strap iron that you are proposing. The plywood is also easy to finish so it blends into the wall and will do a great job of holding the screws that secure the TV mount. On the other hand to attach the steel strap iron to the TV mount you'll be using nuts and bolts and thus the strap would not sit flush to the wall.
I just finished mounting my tv with 16" spacing between studs on center. I cut open the wall and installed 2 - 2x6 blocking (broad face facing out and 1 above the other) with pocket screws in between the studs and then screwed a piece of 3/4" plywood on top of the blocking and closed the wall back up. My tv mount is screwed into the two studs and the plywood/blocking (did this to ensure that the off center tv mounting would be strong enough) and it's rock solid!
Sounds like a true DIY project.1/8 inch thick flat steel stock should be adequate. Am I seeing this right: one length of steel above the other (spaced accordingly), attached to the wall framing with HD screws through holes in each piece of steel? As long as the wall framing is sound and secured properly, I'm confident it will easily support the 60" and it's bracket. But install the steel plates first and then the TV bracket and lastly the 60". Also check the weight rating for the TV bracket.