About to build my diff- What limited slip?

I would use this. It's like a Torsen, err Tru Trac, but supposedly more reliable. Call Cass and ask him about it.
Mopar 8 3/4" (8.75) Helical Gear Sure-Grip ("Sure-Trac")
My buddy has had a Gleason Torsen in the Dana 60 in his '70 Cuda for more than 30 years. He's never touched it since installation. Super smooth, full-time Sure Grip. It's a 440, 4 speed car, and he has been known to beat on it.