My cousin learned scuba about then. I recently asked him about is instructional path. He said 100% of his instruction was provided by the salesman at the sporting goods store that sold him his gear. The instruction was done on the sales floor as the sale was being consummated.
My dad taught me, with a half dozen dives more than me. The good news is that I had to read and was tested on
The New Science of Skin and SCUBA Diving, which was the SCUBA training manual of the day for YMCA and the basis for the training manuals of the SCUBA agencies. Since there was no need for certification in order to dive the quality of instruction was, shall we say, all over the board. My dad got the equipment from Sears mail order, and it contained a little instruction pamphlet to teach the recipient how to dive, he picked up the "New Science..", book to learn from so I was lucky to get better training than many.
2. Spend 20 minutes at 100 feet on air, and you are within NDLs on the PADI tables (3 minute safety stop required), but if you spend 25 minutes (as allowed by the old Navy tables), you are in serious emergency decompression procedures.
You should decide what algorithm you are using just as you would a computer as one may put another into deco on the same dive. In addition, the Navy has had a few revisions to their tables since then as well, so the comparison may be a lot closer.
As for diving, I used the old Navy tables until I got a computer in 2000 something, the one issue I did have was on me and not the tables. I never did get a hit when deco diving on the tables, but I was much younger then.
If the equipment and training for deco diving was as good then as it is now, I probably would have continued on tech diving.
Ascent speed was 75 fpm, then 60 fpm, now 30.
In the US it was 60 fpm from before I certified in '62, until it changed ti 30 fpm. The USN wanted a standard ascent rate for SCUBA and hardhat so 60 fpm was the compromise. Other countries may vary.
Bob