RIM Tucking

I currently have a 2/4 drop on my 99 obs sierra, i am about to do a 4/6 drop. I am running KMC SS's 20x8.5 with a +10mm offset and im not sure the back space but they stick out the fenders about 1/2". So im looking at new rims. What Offset and backspacing should i be looking at to tuck. I eventually plan to bag the truck but for now its just gunna be static dropped. Any Help would be greatly appreciated. Thanks Matty.k

BUMP

i use to run 22x9.5 with 20mm offset on my 01 and it tucked fine but was really close to the bedside in the rear when i bagged it..

BUt i have an OBS

BUMP

didn't you just get new wheels cuz the last ones wouldn't tuck?