Stop in for a cup of coffee

dukeboy_318 said

Yeah email Cass at dr diff. Cass is THE subject matter expert. No offense to Matt as mat is very knowledgeable as well. But Cass has been dealing with these things on a daily basis and that’s why he’s Dr Diff. Outside of this forum , he’s one of the very few I’d trust in anything Mopar

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Also about whether the GL4 or 5 is appropriate. It looks like GL5 was the spec, at least without suregrip.
You could also email Widman. While unlikely to have experience with the DANA rear behind a hemi, the Dana Powerlok (suregrip) was widely used, and he's seen lot and lots of stuff torn down and examined. Being in Bolivia he has nothing to sell. He's just posting info in English to be helpful to the old car community.