Conventional wisdom is double diameter for passive intakes.
That's not very accurate... maybe you knew what I meant.

"Double the number of ports" (same diameter) is the recommendation. Looks like your exhaust is actually 3" (with a 4" pickup). So, 2 x 3" intakes, minimum. More is better, if you can keep the light out.

Plan looks do-able; now's the time to test it for ventilation, temps, and light leaks, before you get all green in there. Good luck! :thumbsup: