If you can change over to the 9'' without a lot of pain that would be better. Like I posted, ford thought it prudent to upgrade the 8.5 to 9'' and some broncos got 9.375''. But if you run the rpms past 6,000 often, the pressure plate can explode, the 8.5 seems better in that area, it has been a long time since I ran a non sfi clutch and parts may be better now.