Your horns are different to mine Norman but on mine the support bracket does sit directly on top of the gearbox and goes across both bolts. It’s basically a piece of angle iron with the horizontal face bolted down to the gearbox and the horns are bolted to the vertical face pointing forward.
BTW can I suggest that you source a Gates NM ‘notched’ fan belt as given the size of the small pulley your standard belt is likely to crack within a couple of thousand kilometres like mine did. The notched belt will run around the small pulley far easier with less stress on it as it’s far more flexible.