Rear pump driven by the output shaft, and getting a custom converter is getting tougher for the small-hub early A's, which also had smaller input shafts on the 904's then.
Anyway, push the car in neutral then push the drive button, the system is pressurized by that rear pump anytime the car is moving,........unless You grenaded a u-joint!!!
I was reading through the shop manuals that I just purchased and it indicates push start in neutral and then push number one for low gear. I see now that the shop and parts manuals will be very handy.