I'd like to mount my 40 lb TV over the mantelpiece, using a flat-plate type mount (Simplicity SXDP3). With a stud finder, I have determined that this area of the wall has studs running horizontally, rather than vertically. (There are vertical studs to either side of the fireplace, but none in between, that I can detect.)
I'm thinking of mounting the plate with the top bolted to one of the horizontal studs, and the lower part attached to the drywall with toggle bolts. Would this be reasonable?