The Rover P5B, Rover P6; and the Rover SD1 each shared parts with the Range Rover.

Like how Jeeps have always mixed and matched parts from other vehicles, Land Rovers have mixed and matched parts from other Rover products; and the Toyota Land Cruiser has mixed and matched parts from other Toyota products.

The Rover P5B, Rover P6, and the Rover SD1 were powered by the Buick V8; along with the 4-cylinder gasoline and diesel engines and the 6-cylinder IOE engine that had also powered the Land Rover Series/Defender.

Production of the Rover SD1 had originally commenced at Solihull in a newly-built wing of the plant dedicated for this passenger car, then British Leyland (Rover merged with many other British passenger car manufacturers) had moved the production of this car to the BMC plant in Cowley, England; and then this East wing of the plant was mothballed until the Land Rover Discovery had gone into production in 1989.

The Land Rover Series/Defender had always been built by hand in the original section of the plant since it’s inception in 1948, and the Range Rover has always been built in the North wing of the plant that had originally been built for production of the Rover P6.

Video about the development of the Rover SD1, using some Land Rover parts; of course.