Does this 17"/18"setup seem like it will work?

If I'm not mistaken BBP backing plates will widen the track some. I'm running an 8" wheel now with -6mm offset. (15x8 cragar). According to the calculator I'm using I'll have .75" less on the inside and .25" less on the outside. That doesn't take into account the BBP brakes. My last duster I was able to squeeze a 275/50r17 on a 9.5" wheel back there with no modifications, but I can't remember the offset of that wheel. I think it was 8mm with a backspace of 5.56