No the overdrive will not fit on a series transfercase, Range rover transfercase is much bigger than series transfercase and the gears inside are not similiar at all.
You can pick up a good III overdrive on the ol' Ebay for around 200/260 quid if you're careful & sound out the vendor. Nope that Rangie stuff will not fit unless you fancy writing a paper for your engineering degree!
I'll have a very good spare series overdrive soon which I'm taking out of my S2, fits straight on a S3 gearbox. Complete with instruction manual, spare gasket, linkages/knob and I think a new locktab thing as well. Hampshire.
What do I have to do to become a non-Junior member? I'm starting to feel inferior. What's the next step? Pubescent?
Here at LandyZone we have plenty of very knowledgable members so if you have any questions about your Land Rover or just want to connect with other Landy owners, you're in the right place.