I had some time to dig into this a bit farther and figured I'd post my results for those that have expressed interest in doing the swap.
The dimming of the 97 ECC control head can be achieved by removing the PPL/WHI wire in position 2 and relocating it to position 10 in the ECC control head connector. Cut the wire down from the connector about 6" to 8" or so and splice into the DK GRN wire in C1 position 6 in the radio harness. Thats it.
The ECC doesn't appear to have an infinitly variable dimmer though. When the parking or headlights are turned on, it dims one level. Turning the dimmer control dims it two additional levels and then completely off. I believe that this is the way it actually functioned in the 97 but will need someone else to confirm.