Wheel and tire selection

[Gumby83]

Hey fellas, im having a hell of a time trying to figure out what i can fit under my stepside. I am looking at 16 inch wheels (for disc brake clearence in the future), i want to run a 9-10 inch wide wheel with maybe a -19 offset. more if i can. i measured off the mounting face for the wheel (off the brake drum) and came up with 6 inches before my fender wouldnt clear. so im wondering if my math is right on this... 10 inch rim with 0 offset would be 5 inches, plus a -19mm offset would be roughly 5.75 inches. does my math work? i really dont want to pull the trigger on this and be wrong. these are online orders.