New here with a just bought 72 Duster 340 car

Just bought this 72 Duster 340 ,,came with another rear end with 8 3/4 center an a 440 fresh build 440 , original drive train gone , but I am going to use the 340 out of my Challenger and put the 340 thats in it an swap to the Duster , I just need an auto tranny or may find a 4 spd setup , unsure yet