For sale is a Matchless G12CS with a 1961 engine. The 1961 engine differed in that they had a much better crankshaft (I bet the1959 engine broke a crankshaft) and an alternator instead of a generator.  The alternator voltage regulator is set up for 12v.  This bike is an excellent restoration and I have owned it for about 12 years and have ridden it very little.  As you can see, the bike uses the competition frame and tank and has a crossover exhaust system with one muffler on the right.