The sutds should be positioned at 600mm centres and will be 50mm wide so if you can find out where the studs are cut out a square of the plasterboard 700mm wide and as high as your bracket then replace with some mdf or other timber and fix your bracket into that!
I wouldnt reccoment using the studs for fixing into as the threads may pull through the studs in time as its only made of tin about 1mm thick!
Any more questions feel free to om me , ive been builing metal stud partitions for 7 years
Jon