Larry,
A quick check of Chevy Parts Catalogs
Radiator shroud info shows 2 different part numbers for 1955-57 and 1958-59 trucks.
Diagrams from my 1966 Chevy Special Parts and Illustration catalog (attached below) show the 2 different truck year groups and the appearance of the radiator shrouds. They seem to look nearly the same, although the 1957 diagram also shows a shroud extension (the 1958-59 diagram doesn't show an extension) that could help with your fan positioning and proper air flow through the radiator.
Not sure the later stock 1958-59 shroud (without extension) pictured would improve your fan spacing and air flow???
Maybe a reproduction type like being offered by
1955-59 Plastic Shroud that looks to have a deeper formed shroud might be the solution you seek???
Hope this info may be helpful???
Dan
