OK, 2 schools of thought from the factory.
Chevy trucks with the 8 used the same rear crossmember as the six cylinder trucks. This caused the V8 to sit to far back to effectively pull air through the radiator. A fan shroud was used to overcome the distance.
As far as 55 to 57 there was no fan shroud used. The radiator support was moved back and a spacer plate installed between the hood latch and the support.
