Wheel Size?

[ls1c10]

Hello I'm about ready to order my rims for my project. I know that its been talked about before, but what would be the correct bs for the boss 338 20x8.5 and 20x10 on my setup. I was thinking 5.25 and 5.5
I'm trying to get the deepist dish as possible

Heres the specs on my build.
-71 fleetside short bed with 4" mini tub and bagged
-cpp control arms
-mcgaughy big disc brake kit with 2.5" drop spindals
-68 rear axle with mcgaughy big disc brake kit.
Thanks