[V8] ATU AYU difference?

[Rosser, James]

Does anyone know the major differences between an ATU and AYU 018 transmission? 

I have a AYU that I've pulled from a 1990 V8q that was in an accident. I'm pulling all the good parts from this car and putting them on a higher miles 1990 V8q that had a clean body This came with an ATU code transmission. Just wondering about the major differences between the trans codes. My initial research says the output flanges are different lengths, requiring different length axels. I can't confirm this but I remember seeing different inner cv joint length between the two cars (never measured, just looked longer); the triple square bolts that hold the cv joint to the flange are definitely different in length. 

Thanks,

James