I believe it is what they now call the S-4. (At the time they did not have nearly so many models.)
The leather is obviously high quality, thick but still supple (how's that for a cliche?) and it is top quality leather throughout - I have seen many cases where the handles, reinforcements, etc. are of lower quality material. The scratches and dings just add character rather than exposing unfinished leather - is that a function of the leather finishing or quality? I don't know - and all of the fittings are solid brass rather than coated metals. And the stitching is perfectly even, and done with heavy waxed thread.
The short version is that it is one of those things which has always done the job, continues to improve in appearance with age, and will outlast me without question. It was too much money even then - I don't think I would spend it now - but I am glad to have it. (In thinking on it, though, it occurs to me that I haven't seen it or the pre '64 Model 70 contained therein in quite some time. I will have to hunt it up when I get home tonight and see about some pictures for you.)