The only dimensions I have were printed in 1955, but might be valid for a
'58 since it is the same basic body. Two suggested locations are shown for
C and K body. Measure up from bottom edge of door 26 1/8" for the forward
location 'A', or 25" for the rearward location 'B'. Lay out this center
line first. Put the front mounting hole on this center line 1 1/2" back
from front edge of door in mirror location A, or 14 1/2" back in location
B. You could lay these out and have a helper hold the mirror in place  
while you sit in the car and test them. Most owners usually just wind up
positioning the mirrors so they can actually see something in them!

There is NO place on the door of a Hawk where BOTH outside mirrors can
be esthetically pleasing...AND be functional.
Several factors come into play:
If you mount each mirror in the same but opposite location on each door-
   A: ONE will not be fully functional.
   B: They both will be functional- but look stupid where they are located
   C: They will look good... but you can't see much from the passenger
mirror IE: vent window frame in the way- OR the vent window cannot be
opened fully...
   D: You mount each in a different location on the door (functional-
but not pretty...)
 
Ray  <- puts them where they "look" good.... and you can use the
driver's mirror  Passenger side is a $150 ornament