Sorry Colin, I've been in the windscreen business 36 years and I can tell you they are definitely different! I have HB laminated screens in stock at the moment with a tint at the top and HC laminated clears on order if you need one.
This was really an enquiry about the windscreen rubber seals.
The ebay seller in the above link is selling windscreen seals for HB Viva. I pointed out to him that the picture in his advert shows a screen and rubber seal marked 'HC Viva'. I asked him whether the seals he is selling are actually for HC? He replied that the two screens are the same!
I was pretty sure they aren't but thought I'd better check before responding to him again. It looks like he's selling HC screen seals as HB items!
Well, you CAN use a HC rubber, it can be made to fit, but they are NOT the same! A better rubber to use would be a mk2 Cortina item, in the past we used them on just about everything, Alfa-Sud's, Fiat's, Viva's, Hunter's and more! If you need a hand to fit it give me a shout, you're close enough for a social. I'll fit it, you make the tea!!