Th plan is using the knock sensing capability of the vems unit. But there is small usable info in wiki.
The original 2wd computer has no knock sensor, but the next version the L8 in the 4wd Sierra has it. Unfortunatelly no info about the working mechanism and parameters.
The place of the sonsor is at the bottom end of the block at cyl 4. This is the hottest cylinder, but I think it isn't good place.
The bore of the cylinder is 91 mm so the theoretic knock frequency is 900/(pi*r) = 900/(pi*91/2) = 6.29 kHz
I made wrench test, knocing the block with wrench and record the signal with laptop by this simple circuit:
This is the wav file:
And the spectrum by Spectrogram 16:
First hit the block at the bottom where the knock sensor is but opposite side, then at the middle of the bore.
I can't decide the self frequency from this record.