Simmonds used to do a stud to easy fit conversion kit where, I think, the screen had a bOlt on frame atthe top to accept a matched fitting on the hood end. Shame they stopped and just do steering wheels now.
Which was exactly what I was going to say, basically it is the header rail of his hood attached to the existing hood, I suspect it still won't be cheap though because a) Its Steve Simmonds b) I "think" a new windscreen frame is required.