Your rear end is either the 7.5 or 7.625 ring gear. Short period of time before it's resting on the side of the road. The 8.5 S10 rear end was so rare as an option, I seriously doubt you'd find one cheaply. Other 8.5 rear ends can be used with spring perch change overs and getting one that the over all length is close. A lot of blood sweat and tears.