I've been running a new distributor in the B for a while but am keen to get the original one back in. You can what year it s from the engraving on the side; mine says 2379 which is the 23rd week of 1979.
To make sure it was running as well as possible with no slop in the springs, I had been thinking of sending it off to the Distributor Doctor for a while for a complete run through including new springs and seals, full calibration as well as a good clean. This service also includes a curve graph which can help with timing the engine.
I'm glad I took photos of the distibutor before I sent it off as when it came back the difference was stark and I had to double-check the year code to make sure it was the same one.