I looked. It is titled the "PADI Standard Safe Diving Practices Statement of Understanding." In rev 5/09, v. 2.0, paragraph 3 lists required equipment:
- Bc with power inflator
- SPG
- Alternate air source
- Dive computer or tables.
Of those 4, in '70 all that was available was that last item, a dive table. Most of us survived. Many of us did stupid, unsafe things before we knew any better, but diving without a BC was not typically a problem because we learned without any such aid.
My very first experience with a BC was a near disaster, since I had absolutely no training on that new fangled contraption.
I still know vintage fans who safely dive the simple "Sea Hunt" style in warmer waters, double hose, single tank on a back plate, no buoyancy,
SPG's certainly made monitoring your gas more simple, but we dived without for quite some time, learning to predict our consumption pretty acvurately. We did have a J valve on our 1st stage, to add a bit of safety edge, in case we misjudged our consumption.