I am doing a 4.556 on mine but with a twist. The crown and pinion will be shot pinned and get a nice isotropic treatment for extra strength. Also, I know some of the bearings from Supra MK3 diffs will fit so I am in the process of getting some of that goodness too. (more strength) if anyone has done that and has the parts numbers please let me know.
The carrier will be treated with heath dispersant coat and also install a nice Aluminium cover with 1l increased capacity. I have STI bushes waiting to be installed at the time as well as a nice Axle Exchange Aluminium driveshaft.
This will be the mother of all diffs! Will post pics and info once is done!