the ratio marked on the case is unreliable as a lot will have been rebuilt and gear ratios swapped. i have 1500 spitfire gears in my modified 2.5 pi vitesse. no idea what power it made. but i once had 6.000 rpm in overdrive, it would have done more but i bottled it.
Yes good point, but then it is just a case of turn the dif and count the turns on the output shaft? I seem to remember that's what you did, but it is so long ago!