Hi Mark, of course you're right, I got it altogether wrong with the case! I must've got confused by the right-hand crown...also hands are very different from 501.50x.
Indeed a very nice watch, though I've never seen it in the metal.

As for a switch in policy "from names to numbers" I don't know, the same catalogue (1985 if I am not wrong) had a lot of named ones, and in the same series, or at least bundled together under the "1000 series chronographs" section, we had the L5100 Carreras and some (wonderful) Cal.12 Autavias, but indeed we had the 510.50x, the non-Monzas, and the non-Cortina L5100 as well. So really a mixed bag for a confused and convoluted period for Swiss watchmaking industry in general and Heuer in particular.
And still, at least IMHO, Heuer brought out in this very hard period a series of gems that are among my personal favourite: the 510.50x above all, the L5100 Carreras (especially the black PVD one 510.511) and the some of the most beautiful Autavias, the silver dialled, the black PVD etc...ah, what a time!
Cheers

Fabrizio