B/S on Coys 20"/22"

[82ChevyC10]

Hey guys, I'm looking to install a set of the Coys C5 in Black Chrome. I want to run 20's in the front and 22's in the rear. Currently I'm running 20's on all fours with 275/45/20 tires. My truck is dropped 3" in the front on spindles, and 4" in back...but will be going to the CPP rear trailing arm conversion and lowering it an extra inch to level out the truck. I like the look of the front but the back just isn't cutting it, the wheel spacing is too narrow in the rear, even with 2.5" spacers. I'll be going to 285/45/22s in the rear and hoping to not have to run the spacers. This should give it a nice rake. Since the the 22's are available only in 5" of back space, my question is what would be the proper back spacing to get on front 20's in order to have the same track width front and rear?