I have an 80 d150 that I have slated for a 6bt. I also have a late 60s 8.75 rear. I'm a big 8.75 fan and have never hurt one when it was set up right. I never put one behind a 6bt though. It's what I have so it's what I'll use and I expect to be reasonable with it, and I don't think it's a dana 60 and won't treat it like one. So having said all that, anybody here put an 8.75 behind a 6bt? Any insights?