Non-lecture:
The first streamlined Lotus sportscar was the MkVIII (1954). Its replacement was the MkIX (1955). Both were powered either by 1500 MG engines or, latterly, 1100cc Climax FWAs (and yes, there was a 1½-litre Connaught-engined car or two as well)

The MkX was built to take the bigger (2-litre) Bristol engine