In late 1957 a new derivative model was introduced, using a , Excelsior three-cylinder 492 cc engine with triple carburettors. This engine configuration was made possible by the vertically split crankcase of the Excelsior engine and modular crankshaft and barrels, which made adding a central cylinder relatively easy. A four speed gearbox was standardised. The top speed was now . Production ran from October 1957 to March 1959 with chassis numbered 1 to 666. From about October 1958, in order to coincide with the introduction of the 'Foursome' (see below), they were renamed the ‘Twosome’. Also at the 1958 Motor Show a Fixed Head (or Hardtop) was announced and displayed that had external as well as the usual internal door handles, but there are no records that this body style actually reached production.