42RH / A-500 in a Duster with pictures.

Look at the trans picture on the second page of this thread- There is a 3 pin plug, natural in color near the neutral safety switch. The 32/42/44 RE transmissions have a black round plug there with 8 pins and are to be avoided. They have an electronic "governor" and is useless for this application. People have had good luck running the earlier version called the A-500, depending on what you are going to do with the car and level of power that could be an option in case you don't find a 42RH. It can have upgrades done to it as well but it is best to start with the best revision in my opinion.