Resource/database for Longines references?

Compared to some other brands, it seems that Longines had an awful lot of different model references, often multiple ones for watches that superficially appear to have identical case designs.

For example, as far as I can tell the references 7950, 7951, 7952, 8300, 8301, 8302 and 8348 all relate to one particular style of 37mm vintage Ultra-Chron case. I wonder, did the references change for different case materials, or even different dials / hands?

Maybe a niaive question, but is there a comprehensive list anywhere of reference numbers with information / pictures of the models they referenced?

I very much like watches from 1970 and 1972, in fact that general period (latest 60s and earliest 70s) is the focus of most of my collecting. I know those links (in fact it may have been you who introduced them to me a while back!).

Yes, from these and from internet image searches I think you are right. 8301 is steel, 8302 is rolled gold, and 8348 is solid 18K. I happen to know that 8300 is also solid 18K.

In the 1970 catalogue, 7951 is steel, 7952 is rolled gold, and 7950 is solid 18K. So that follows the same pattern, with the last digit indicating the case material (0 = 18K, 1 = steel, 2 = rolled gold), except that 8348 and 8300 are both 18K...

The 75xx series seem to be earlier and replaced by the 83xx series, but they look the same to me. Some of these watches have casebacks with the Longines / Ultra-Chron logo in the middle of the roundel, others have a plainer roundel with circular text, but there seems to be no obvious relation to 75xx vs. 83xx (although I haven't seen any plain case back 83xx).

There doesn't seem to be a relationship to the dial or hand variants either. There are two subtly different common dial variants, one in which the chunky markers have a narrow flat line in the middle that lines up with the minute marker behind, the other (more common) where the surfaces come to a sharp line in the middle. I think there are slightly different hands associated with these variants. Lumed dials have four rectangular lume dots at the ends of the cross hair lines and lume windows on the hands, and there seem to be both lumed and non-lumed versions in both the 75xx and 83xx series.