Additionally, correct me if I'm wrong but, I read from a magazine that one of the reason's the 400s and 440s were kept around through the late 70s was because Chrysler Corp was going to build a "Ball Stud" Hemi off them but, due to regulations and financial pressures the idea was scrapped but, also it is one of the reasons the 400 was also built with a thicker webbing in the block in mind.
