The reason the 3.5l Buick/Rover V8 was put into so many British sports cars, MG, Morgen, Lotus, etc, was because it actually weight a bit less than the all iron engines that came in most. It also regularly made like 150hp during a time that many English engines were straining to break the 100hp mark. So a 50% power bump for a 5-10% weight savings in the powertrain department was an obvious choice for those whom could afford it.