diff. ratios . sedan & gt. numbers stamped on housing under filler plug vertical raised section no,s should be 10-41(4.1) 11-41(3.72) 9-34(3.77) and possibly9-37(4.1) two of my diffs have only 1-41. assume these are 4.1 ratio hope this info is helpful

just to add....
the number purtain to the number of teeth on the crown wheel and pinion in the diff.
34 or 37 on early crown's, 9 on the pinions, and 41 on the later crown's with 10 or 11 on the pinions.

the "9" numbered diffs are from early sedans and PR90's only. the really really early ones also had the oil drain plug directly under the fill plug, not in the rear cover as later ones did.
the others are from mid-late cars, and are a stronger diff by vertue of more teeth on both their crown wheel's and pinion's.

lindsay, you'll find urs are "11/41", being 3.72. 99.9% of aussie delivered belletts had these, and the 4.11 was an option that i have never seen fitted to an aussie car.
i have seen a 9/37 4.1, but only one.... and it's fitted to a well known car down here.
stories went around years ago about factory auto cars having 10/41 4.11's.... but every auto i've been under has had a 11/41 3.72....
cheers.