The 43/13 tag is the number of teeth on the pinion and the crown wheel.
If you divide 43 by 13 you get 3.31 so that is the ratio.
That should be fine for a Rover engine. I have a 3.54 in my Chevy powered car and you get great acceleration but a bit less top end speed.
If you can turn each wheel independently of each other then it is a standard open type diff or it's a completely knackered power lock one!
Craig.