91> Speedo sensor

[1972_911T]

Hi guys ive just acuired a 964 trans to transplant into my 911, I was under the impression that the 964 speedo worked the same as on the early G50's but after further investigation it seems in 91 and later G50's this changed from the sensor on the side of the diff to something else, however im having trouble finding out how it changed. How does the speedo work on these cars as there appears to be nothing on this trans in the way of a sensor.

Thanks Steve