I would tune it with a wideband.

As for plug color I've done that on 2 strokes but had to cut the threaded section of the plug off to get far enough down on the porcelain to see any color.

I think if you're looking for color on the entire porcelain section of new plugs chopping the engine after the traps you'll end up pretty rich.

69 Charger. 438ci Gen2 hemi. Flex fuel. Holley HP efi. 650rwhp @7250 510rwtq @5700