Thanks Beemerboff, I have now taken the plunge and drilled the housing and got the windshield on and all good. As you suggest the place to start is the top RH fixing which is on the front of the headlight cowl above the housing.
For those of you wanting to do this, the problem is here is no way to mark the drill point and the is no indication on the inside of the cowl. To overcome this I put double sides sticky tape on headlight cowl where the mounting points were likely to be and “stuck” the wind shield in place to get the perfect positioning. Before doing this I put a thin ring of blue tack around the mounting point for the upper RH bolt which stuck to the tape on the headlight housing. I used this as my guide for the first hole and drilled. I replaced the windshield back on the headlight cowl. Fixed it using the upper RH bolt and the sticky tape for the other areas and marked there holes.
The bolts for the fixing kit are 5mm but I drilled 6mm to give me some wriggle room (which was needed). Drilled, bolted and hey presto done.
Thanks for all who replied....I love this forum...always people happy to help.