truck 12 bolt pinion pre load

[blazer2007]

I have a 1980 chev truck with the 8.75 12 bolt rear diff. I can find the pinion pre load but can,t find the final pre load in inch pounds. I,m using a new outer bearing and used inner which is only 3 yrs. old and looks really good.I caught the outer one which is just starting to pit. Pre load says 13-15 new and 6-8 old bearings so where should I set my pre load