Please help Centerline wheels and rear adaptors Who knows which sizes to use

[72 Cheyenne402]

I'm finally going to order some tires for my truck (285-50-20 for the rear and 255-55-18 for the front) doing 18x8 with a 5.0 bs and the rears are 20x8.5 with 5.4 BS but the outside to outside measured with is 20x9.

Should I run a 1.0",1.30" or 1.5"

Any advice would be helpfull. right now I have 295-50-15's on the rear with 15x10's