Welcome to forum John, and nice watch.
By most points of reference, Heuer made very little of anything when it came to the chronographs. They were something of a high profile but low volume addendum to a business that was largely concerned with making the stopwatches and timers.
But this watch was indeed likely to have been one of the watches they didn't make very many of even in comparison to some of the others. In fact, it was something of a moot point what to even call it until Stewart inadvertently gave me some info I needed to solve the riddle of its reference:
With regards to the 750.501-3...
Like I say, it isn't in any OTD catalogues, but it is listed in the
OTD MOAT.
When I first saw pictures of them, I presumed they were Black PVD
Pasadenas that had the PVD sanded/polished off. (This is still
the case, you see many '750.501' marked Heuers that are
stainless steel - these have had the PVD removed, probably
because they looked tatty). But, I've seen sufficient
750.501-3's for sale that are in good/mint condition, that are,
or appear to be factory stainless steel. Coupled with the info
in the OTD MOAT, it's solid evidence.
With this paragraph Stewart, you've solved the riddle whether you know it or not!
It was Heuer's model code schema putting them into a bit of a fix. The terminal numeral of the numeric code usually denotes material, in these six digit codes as well as the four digit ones, with some exceptions like the divers. 3 is most common, and denotes steel, 5 is gold plate, 8 is solid gold and 1 denotes a PVD finish.
In calling the PVD 750.501 a Pasadena and the steel 750.503 a Montreal, a problem arose when they wanted to produce a steel Pasadena. Logically, that model would be a 750.503, but that number was already taken by the Montreal. Looks like the compromise was to append a -3 to denote a steel case to the existing 750.501 code for the Pasadena and differentiate it from the existing Montreal. Hence 750.501-3.
Makes complete sense to me now.
In fact, that thread makes a good place to start reading up on the watch and its siblings: http://www.chronocentric.com/forums/heuer/index.cgi?page=1;md=read;id=41052
