Im looking into possibly building an a518 for our 400 horsepower mopar small block scout ii. I figure i probably want stronger parts for it and i keep hearing that an a518 is just a 727 with an overdrive unit so i was wondering what parts actually interchange so i could use parts from a big block 727 i have laying around. I know the cases are different and i dont think the valve bodies would interchange but what about the planetaries and clutch drums?