I've  done more  than  a  few  cars  BOTH  ways.  if  there  might  be  rust  under  the  windshield,  yes  it  should  come out. new England  car  or   west  car???     then   on most  models,  the  whole  dash  can   easily  be  take out. then  you  can  work on  the instrument  cluster/wiring   e asily  for  sure.   
    taking  out  the  windshield ,   depending on model,   can   result in  ya  having  to  buy  a  new   gasket.   $$$$$.  can you    remove  and  install  the  windshield  or  have  to  pay  the   glass   guy??    how  much  time  do  you  want  the  car  apart.  how  long  does  it  take  you  to DO   the  stuff  under  the  dash  with  it  out? 
     is  it  to  be  a  "show poodle"  or  a   driver?  
   like   removing  ALL  the  glass to paint.  yep the   resto  will  do  that  as  they  charge  ya  $80  /  hr?????    for  me,   taking  the   qtr  glass  in and  out  is  always  a  major  PITA !? 
      when it  comes  to  some jobs  on  these  old  cars, what   result  are  you   looking  for???  ans,   are  you  results  oriented  or  " anal   retentive"??   ha