904 trans

I just want to throw in a trans and go but all my working trans I pulled from cars were e & b body. so wasn't sure if a A body 904 was the same length . dot get why they are if the manuals all have different tail lengths why the autos dont but im happy for that answer. MY dart has a 360 does have a 727 behind it , but I dont care what I put there I just want to choose my best trans that will work which is probably the 904 I took from a good running satellite last year. just didnt know it would fit same