Byron originally used the 4.2 Sachs made by A&M with Byrons's mechanical advance and a C&H ignition...The A&M version of a Sachs was compromised by the A&M crank, prone to early failure and vibration. Byron later used the Mustang 50 engine, not strong enough for a 3 blace prop..There is no 4.6 Sachs engine made...If Iron Bay is selling a 4.2 Sachs it must be one of the other manufacturer's versions, and will probably be using a C&H ignition with Syncro Spark, should be fine....