fried my brain with offset calculations....

ok, from what i've gathered so far a 15x8.5 wheel ( and correct me if im wrong, please, please do) with a 4.5 backspace would work with a 6mm offset up front but how about the back? my truck is 2wd metal, cranked torsions and pulled rubber bump stop out, pulled the 2 center leaf's out, sorry i really really suck at math lol, also i tried to check my work with the forum calculators and it seems they're off by about 1 inch or so, thank you in advance im sure everyone hate's these questions

I dunno man a 17" Escalade wheel is 7.5" wide and the offset is +31 I think and it just barely works out back.

dont think he is trying to tuck. pretty sure hes going more for a flush look like me