it seriously looks there is way to much timing on that motor. you need to pull timing out of that motor at WOT, the part throttle looks ok, and the idledoesnt look that bad either. but please pull some initial timing and total timing. that motor is seeing some serious heat, and detonationg. you may want to add some fuel up top as well.

 

Stock NGKs on a boosted Y8 = stupid.

ZFR6F-11 for light boost, then 7-12 psi BRK7E-11.

Plugs have too many miles on them to read precisely, so you can properly match plug temp to engine. She's sooty in the well and clean on the electrode with can mean anything from too hot (yes!) to stupid rich transitional AFRs when the engine isn't producing the thermal load required to use such AFRs.