1600 had a 3.77 and the 2L had a 3.54 ratio diff. If you have the diff centre out divide the number of crownwheel teeth by the number of pinion teeth and there's your ratio. If your lucky there is a tag under one of the bolts around the diff centre. If the diff is still together you could turn the pinion flange one rotation and count the axle rotations, I've never done it this way, I'm guessing.