Originally Posted by davecymru
I've got what I think is a 4:11 in the garage if that is any use?
Many 4.11 diffs are rather weak, it's not even recommend to put a 13/60 engine into a pre 1967 1200 Herald without uprating! The Vitesse 6 used a version of the early diff and was prone to output shaft breakage. They beefed up the output shafts for the post 1967 1200 and 13/60 Herald. I've got two 1200 diffs.
If your diff takes 3/8" (9/16" AF) bolts in the output flanges, it's probably the stronger version (or is the weak Vitesse 6 diff).
Although I will have to check the numbers to make sure its not a 3:89. Any idea where I can ref the casting number numbers?
You can't tell the ratio by the casting number (the stamped tag is probably long gone) and in any case bits have often been swapped around. You need to turn the flanges or count the teeth.