Zenith Respirator X A7632 - some pictures, some questions

I had been after a "Respirator" for some time, and was lucky to find one with the original bracelet in Japan pretty much a year ago. It spent some time at my watchmaker for a service, but has been ready for use some time now, and I have worn it before on a leather strap. Now, I fitted the original bracelet again and must say, it adds to the character of the watch ... So here are some pictures before I have some questions.



And here it is on leather:



The watch is a Zenith Respirator X (model no. A7632) with the 2552PC movement (23 jewels), which was produced between 1969 and 1972. I was lucky to find the model number in a japanese catalogue from 1972 (Nakahiro):



And for good measure, here's a picture of the movement (not particularly large, sadly):

So, I do have some questions. Thought it'd be better to add them in a separate post, so they don't get lost among the pictures.

First, I'd be very interested in finding out the exact year of manufacture. Is that possible from the serial number? The one on the caseback is 542D071 - would be great if someone knows something about this, I haven't been able to find anything of use on the web so far.

Second, the bracelet... It wears comfortably, and I find it adds a lot of character to the watch. The light grey dial with vertical "brushing", the matching brushing on the case, and the 5-pronged folding links on the bracelet, it has a great look to it in my eyes. My problem is that, while I can just wear it, it does fit a bit snugly. Hence, I've been searching high and low for an extra link or two, but have not been successful so far. I even went as far as to doubt that this is an original Zenith bracelet, but the catalogue images for 1970 and 1972 show this exact one, no doubt. Maybe it was only for the japanese market? It is not an NSA/Novavit bracelet.

I know that some bracelets (for Omega, for example) were produced locally in Japan, so that would go part of the way explaining why I haven't found anything.

The bracelet is kind of similar to the Omega bracelets no. 1193 and 2054, but has one extra "prong". Does anyone have an idea where I could find extra links for it?

I would appreciate your ideas, or anything you would like to contribute. Thanks.

EDIT: another picture, showing measurements of the bracelet:

You can contact zenith and get an extract from the archives for $75. It will tell you everything about the watch

Very nice watch.
Here is his black brother