[rotorwrench]

The crab type was developed for the 1942 model Year which was short lived in that the US became involved in the war and shut down auto production in February of 1942. During the war, a more sealed design was developed that became the rabbit ear type distributor with the two piece cap. It was continued in service after the war but it's pretty easy to convert to fit the crab type cap. Some were aluminum and some were cast iron if I remember correctly. During the later 60s and 70s, the rabbit ear type cap components were not available so most folks converted them to the crab type so they could keep the 59 series engines running. Eventually the two piece caps were reproduced as they are today.

The 1941 or 01A distributor was the last of the diver helmet types and the "new" crab for 42 was a one year deal in civilian production. Another thing to watch for is that some were made for the G series 6-cylinder and they are different but similar in appearance. There are adapters available to use 2-bolt types on a 3-bolt cover and there are long cam adapters as well for some aftermarket applications.