Yeah, those are knock sensors in the valley. I discussed the valley harness in my first post on on tearing down the engine.
How many knock sensors do modern Ferrari V12's use?
BMWs sensors are arranged longitudinally, so you may be able to put one at the 1/4 point in the valley and the other at the 3/4 point, then apply some time-domain filtering to the signals. I'm not sure if having two knock sensors is necessary for catching detonation in the first place, for confirming that a particular cylinder is detonating or for filtering out noise to avoid registering false knock.
Your compression is... 10.5? I would say keep 93 in it and don't worry about it. My prior Northstar ran fine on 93 with 11.5 and a bunch of oil in the chambers from bad bore finish. It would pull cleanly and accelerate uphill from 1000 RPM in 5th gear.
BMWs V12 for the McLaren F1 runs 11:1 with no knock sensors at all.
Classic Mark Logic (CML) wants the BEST knock sensor arrangement, which may be four sensors... but even two sensors would be better than zero sensors.
One of the things I haven't understood about knock sensing is that detonation happens with the piston way up in the bore, so the shock/noise has to go through the bore liner, through the water jacket and through the outer wall of the block before it hits most knock sensors. And the head gasket interface can't be very good for transmitting shock, especially with composition gaskets... maybe MLS gaskets are better but still have several interfaces to travel through.
I would *think* that you'd want knock sensors on the head because that's the most direct path for the shock/noise to travel from the chamber to the sensor... but not only does NOBODY do that, EVERYBODY (that I've seen) puts them on the block.
And AAAAAAAACKSHULLY... there is a way to get TWELVE sensors
Spark plug gap impedance sensing/plasma ion sensing... whatever you want to call it. I've seen aftermarket modules advertised that do that. Bugatti does it on their W16 because apparently 45 degree firing intervals are not far enough apart to distinguish with conventional knock detection methods.