Good news is compression came back all pretty good, ran from 149 - 165 across all 8. Bank 1 being a touch lower than Bank 2. Possibly due to the motor being warmer from the cranking? No telling, but I wasn't concerned about the deviation and consider the motor to be healthy enough to continue. Not budgeting for a rebuild or anything just yet.
Spark plugs were all unremarkable, 6 & 7 were a little darker than the rest but they all just looked like loosely gapped FoMoCo plugs. Have some appropriately gapped TR6 in now and the car seems plenty happy now between the fresh oil, plugs and the new JLT intake.
I swapped out the fender-well unit for a straight-shot unit. The fender filter was DISGUSTINGLY dirty, so no wonder the car seems happier.
Didn't get a chance to check through the clutch more, but just still think it's interesting that the noise disappears when the clutch is engaging/disengaging, and really only as idle when in neutral. A tiny rev also stops it entirely. I'lll check more tomorrow.