My filler tube has no nipple for a vent line (never did). I seem to remember that 70's were different than other years. If the vented caps only let pressure (air) in then how is the pressure relieved? If it is through the tube as shown in your pic then why wouldn't that same tube let air in thus eliminating the need for a vented cap? Do some years/systems run with tanks at atmospheric and some under pressure? The body shop manual I have shows a vented cap for 70. I'll try to copy that section tomorrow and post it.