Lowered 1987 3/4 ton

[Silverado454]

Hello everyone, first post here. Ill get right to it, i have a 1987 Chevy R20, and its lowered about 4 up front and a little more then 5 inches out in the rear. Im currently looking at getting some new steel wheels from Detriot Steel Wheels and i have a few questions about wheel fitment. Im thinking about going 20x9 up front and 20x11 in the rear. Right now i have 16x8s all around with -06 offset and it seems up front i could fit another .5-.75 inches of backspacing easily(.25-.5 on front side of wheel) and in the rear i would like to add another 2 inches of backspacing with -31mm offset as this would get me another inch out. Sorry seems like a lot, any help would be greatly appreciated. I realize 20x9 and 20x11 might be too big and if thats the case ill go 20x8 and 20x9(they dont have 20x10s)

Thanks