I don’t see why the ’57 would be any different than the AD’s, the shackle is the same design. The illustration of the front shackle in the ’56 resto-pack shows a washer in place. Anyway, all of them that I’ve seen do use a dust seal in the front. The parts book is a little vague and it is not always 100% correct so I wouldn’t take that as gospel anymore than I would what is printed in a vendors catalog. In the end you need to apply a little logic, ie., does it make sense to seal water and dirt out of the pivot lubrication.
http://www.pbase.com/dennygraham/image/122019804
http://chevy.oldcarmanualproject.com/1929_57chevyparts/57cmpc0585.htm

Denny Graham
Sandwich, IL


Denny G
Sandwich, IL