There are 2 frequencies for the 5.7 and 6.4 Knock Sensors(part# 05033316aa). 1 is 5.9kHZ and the other is 13.72kHz. The frequency used depends on the calibration. Both these are the Center frequency. Hope this helps someone in the future.
Thanks for the compliment! They are Marshall gauges. Marshall makes some really nice stuff, and it seems they put a bunch of different faces in the gauges (and I think other companies use their gauges with other custom faces as well). I know new vintage makes custom faces...