Peter, the 40% locker is the most common with two friction discs per side. The 70% locker has three discs per side and depending on how the suspension is set up, it can cause understeer. Can be corrected with proper anti-sway bars, but the friction from a 70% locker also causes more heating of the ZF lube. So if you invest in a 70% and running the 'Ring in your Pantera's future, consider investing in a diff cooler. With a 40%, just driving 400 miles on superhighways at speeds of 120mph or less warms the lube in my car to no more than 180 degrees F. Higher avg speeds causes more heating.
Thats why when pro racers ran Panteras in the 70s & 80s, they used the earlier ZF sprag-lock diff from the GT-40 (and a few Mangustas & early Panteras). But those wear rapidly and I'm told there are no more ZF spare parts for these diffs. You have to make them yourself. And even then, some racers used diff coolers.