I investigated this a few months ago over here in Melbourne, especially as I've a planned 400hp motor going in.
The engineering firms I spoke to suggested that although they could remanufacture them out of better material, using better techniques, this would only be a partial cure as the actual spline design if the output and input shafts are fundamentally flawed for big horse power applications.
now back at looking at Jag Diffs. I do, however, follow this with interest.
Fraser