[bobcowan]

It looks like Superformance used the Tri-Lobe design like a Ford Thunderbird. IIRC, it also used the Ford 8.8 IRS differential.

If it's a 28 spline diff, you could buy a '95 Thunderbird axles for $120 from Rock Auto, and then swap the axle shafts. That's what FFR builders did for decades.

You can get new ones from DSS. I'd be willing to bet it will be the Porsche 930 style. Which, IMO, is an improvement. That will cost you about $1,700 for the pair. More expensive, but you get what you pay for here. And, they are easily rebuildable.