When did ROW SC engines get a CA air pump?
 

When the car was Federalized or "converted" to DOT or EPA specs by the importer.

Air pumps were added to all ROW Mercedes, Ferrari, Porsches, Lambos etc when they were imported to the USA to meet EPA specs. In order for the car to pass US inspection the cars had to meet or exceed US EPA and DOT guidelines.

Since a US SC had one, a ROW over here had to have one. Plus the airpump on the engine is the most visual cue that the car was "converted" or Federalized and the very first thing that inspectors from the period looked for (ask me how I know). Most people took them off, however if you were in California you had to keep yours on in order to pass.

ROW SC 911s had factory installed air pumps through 1983. Only '78 and '79 US models had air pumps, '80-'83 did not. They were not added on to federalize a ROW car.