I have the quaife diff on my auto and it really transforms the car , i thought about altering the gearing back when I had the n/a car but understood it meant losing the CC which i couldnt do without
Fitting the quaife in the auto is a chore as well , you need different stub axles, nuts. bolts and washers (depending on year) new bearings , seals , possibly shims and then you have the oil and labout , not a cheap undertaking at all