I keep forgetting to grab my sunglasses from out of the car and take a picture, but, I solved the problem with some semi-wrap around sunglasses I had, and some thin foam padding which had 3M adhesive backing on it.
I cut it into a slim length and stuck it to the top of the sunglasses frame, so the foam follows the frame from one end to the other, and it works perfectly, no need for the baseball cap . . . Unless you want to wear it that is, but it's nice to have a choice now.
I think the main thing here is that cars now have shorter screens in front of you, which is where the sun gets down behind the glasses, whereas the Triumph Stag had a longer windscreen / frame that went into a T shape, but of course these cars now are much more open, which is lovely.
I'll pop a pic up tomorrow.