Larry,
It is a very good possibility that the pictures of both the 57 and 58-59 were for "Big Bolts" as much of that catalog is actually directed towards the "Big Bolts/Commercial Trucks". They didn't do a great job of specifying which trucks they applied to so sometimes just have to guess.
Seeing your picture, makes me wonder if you could possible fabricate a similar style shroud extension and attach it to the existing shroud (would need some extra support straps and connection points to prevent separation, but it could help with your air flow management???
Dan
