Black tanks were added by Airstream in the late 50's/early 60's first as an "International package" upgrade then as standard a couple of years later. As far as 12V
, it depends on the trailer, our '56 does have it. What they didn't have was a converter or inverter to change 110 to 12v
- they had two completely separate sets of lights. If it was a park model it may not have had 12V
at all. Again, they changed in the late 50's. Our '64 has both. Grey tanks weren't introduced until 1973.
You can add black & grey tanks to earlier models...we are doing so with our '56. It's not for the light-hearted, but entirely possible to do - especialy if you have to repair or replace the floor.
You may find these two websites helpful:
Vintage Airstream Features
Vintage Airstream Photo Archives