If it has a 60 in the rear you need to buy gears for a Dana 60.
I don't remember what year they started, but it might be a 10.25" Ford Sterling.
You definately don't have an 8.8". As BenXJCA stated look for drop out third member to see if it's a 9". I would strongly suggest bulling the Bill of Materials off the axle and identifing if your not positive what it is.
Later,
Lincoln