69 is pretty meh. I recharged my factory system with R12 prior to a long road trip back in June. I also installed a ball valve in the heater hose that goes to the heater core (if you do this I recommend you install it on the return line so you don't have hot coolant recirculating through your motor continuously).
With the valve open and coolant running through the heater core, I was getting 52 degrees out of the vents. With the valve closed, I got down to 34.6 out of the vents at one point on the trip.
Due to a silly and expensive mistake on my part, my r12 all leaked out, so I have since recharged with enviro-safe 12a (ES-12a) which is a propane blend. With the valve open it will drop down to around 54, closed 66 or so. I've never retrofit R-134a into a datsun, but 69 degrees sounds almost like a waste of time, especially if your car has t-tops.
PS - When charging an auto A/C system have the blower on full blast, the windows down, and the car idling at 2,000 rpm.