Where do the knock sensors go on a 6.0L iron block?

It depends on the block generation:

• Gen III 6.0 (LQ4, LQ9): one-wire sensors in the valley under the intake. ICT's 551216-KN30 relocation adapters move them to the side of the block (with extension WEKN030-60).
• Gen IV 6.0 (LY6, L96): two-pin sensors on the lower sides of the block above the oil pan rail, one M8-1.25 bolt each. Adapter 551216-KN40 + extension WEKN040-12 can move both to one side for clearance.
• Gen IV sensors on a Gen III block also works, with wire adapter WAKN034-36.

Standalone ECUs often run with knock sensors disabled; with a stock GM ECU, keep them working.