The Matchless 600cc G11CS and equivalent AJS 30CS were produced in 1957 and 1958 and differed somewhat from the "standard" models G11 and 30. Engine differences were primarily the high compression pistons fitted to the CS models. Mechanically, most of the CS’s were fitted with folding kickstart crank and siamesed exhaust system with silencer on the right side. Trim wise, the CS twins were almost identical to the CS singles with quick disconnect headlight and the small Lucas 529 tail light. Aluminum mudguards were used in place of the bulky valanced guards fitted to the standard models. Also fitted were a smaller petrol tank and a seat that was shorter than that used on the standard models. While we think that most of the 1957 & 1958 CS twins had the usual "CS" in the engine number, we know that some were imported to North America in CS trim but without the CS designation in the engine number. Either that, or the dealer or importer spent a small fortune fitting new mudguards, seat, lights, petrol tank, etc. prior to sale! We know of at least two very original 1958 G11 twins here in the States that are fitted with all of the CS goodies but neither has a CS in the engine number. 1958 was the final year for the G11/model 30, being replaced in 1959 with the 650cc G12 and model 31 variants.