So I've decided to replace my entire m416 axle with a custom 3500 pound axle. the wheels are we using are 15x8 with 3.75 inches of backspacing. Formula I have read is take the width of the frame and add to that two times the backspacing. and then add an additional 1.5 inches for each side. That would equal 7.5 in backspacing and 3 in "extra space". So at this point I need an axle that is frame with plus 10 and a half inches. Does this sound correct to everyone?