"a mistake"?? isn't engineering situation-specific and
evolutionary? would the "smaller radiator, smaller fan, and smaller grill currently found on everything" work for an otherwise stock TF truck? why would you want to use a shroud that
restricts air flow all of the time instead of a "duct" to
enhance air flow under the conditions that's useful, without restricting it other times?
we
are talking about 40+ year old vehicles [with the frontal area of a barn] and 40 year old technology and making them work dependably as designed

Bill