Porsche has used several generations of the Bosche Motronic DME since the introduction of the 1984 911 Carrera. The nice thing is that Pin 6 of the DME is consitently used for RPM signal through the Carrera years to 1989, the 964 model years, and the 996 model years to 2006.
The 997 model introduced substantial changes to the EMS, and the whole brave new world of fly-by-wire throttle control. I'm just not sure that P6 is still RPM on the 997 ECU, but its high probability. I'm sure there are some 997 pilots out there who can verify this.