1971 plymouth Duster help for this vin decode!!

Hello everyone I’m new here and this is my 71 Duster that I’m planning on restoring. Car has the original engine but not the transmission and I was looking to buy a 4 speed but I think this car came with a 3 speed . I think 3 speed was produced less or I’m mistaken. Need it some help with this vin tag. Any help I will appreciated
Thank you