Not an H28. We know about those, they appear in the catalogues. Here's one, albeit a 1589 B with white dial in a 1979 catalogue:

And that's the thing, we have pretty good documentary evidence throughout the 70s in respect of brochures and price lists. That decade is probably the one we are most confident on in all of Heuer's history.

So when we encounter a watch we haven't seen, we look for precedent in all the elements of the watch. Which is what I did in that post I linked earlier.

http://www.chronocentric.com/forums/heuer/index.cgi?page=46;md=read;id=39407

And it came up short on pretty much every front.

And even those French models aren't above reproach; all the components were available to buy easily a few years back and a good few watches were assembled after the event. So all Heuer components, but put together by someone other than Heuer or their contracted partners long after the original watches were made.

I'd really like to see the watch being discussed in a catalogue or price list before I could be convinced, there is so much about it that feels a bit off.