I would go up 2 jet sizes on fuel for your wet kit and spray it in 3rd gear after the cars has really warmed up. Any hint of detonation, get off the throttle.
I did this at the track and pulled over on the return road and checked a few plugs. Look for melted electrodes, melted porcelin, sparkles from melted aluminum. The tips of my plugs are white, but there is a little grayish tinge to one specific spot on each plug.
Oh yeah, no more 87 octane.
I run Sunoco 94 just to be safe.