408 tuning with a Wideband sensor

Cool.

Set the idle where the engine likes it. Not necessarily to a number. A vacuum gauge might come in handy for this. See where it pulls max vacuum at leanest point.

Work on the mains, maybe step down two sizes and try a drive. I wouldn't mess with the main air bleed until you get the main jet size in range.

Nice deal, fuel mileage will go up quite a bit... not that it's the reason we do this stuff!