Re: Pickup and wiring upgrades for Ibanez RG321MH
Just want to point out middle position where you "don't like the sound of two humbuckers together". #3 both parallel is essentially both in single-coil but with hum cancelling. Parallel makes for a single-coil like sound with the other coil used to eliminate hum. I'd leave it wired as-is personally but YMMV.
Then you can add a push-pull to make single coil.
I personally like Alnico pickups. The Mahagony body (dense/warm) can muddy tone without the maple cap so that throws a monkey wrench. You might need more highs than a PAF PRO for example allows.