Will these tires fit?
 

Ok so i am on the hunt for bigger tires and may have found a candidate.

Chrome Wheels and Tires

they are 31x11.50/R15, in the post he says they came off of a 1978 2wd pickup
I cant locate the backspacing on the rims.
I am concerned that the 11.50 tires will be too wide without a decent backspacing, i would love to not rub at all. Currently i have the 235/70/R15 stock rims on my car, with a 1.5 tbar and 2 inch shackles and a 2 inch body lift in the box next to me ready to go in.

I searched the forum for a while but its late and i am tired and could find enough info....

Any input is greatly appreciated :)