Tim/anyone,
  I'm not challenging the differences - but I have a question ...

  Why would a railroad order/use a 5/6/6 -vs- a 5/6/5 -vs- a 4/6/6 ... etc.?  Other
than a spotting freature why did Youngstown make different configuration for 
a "nominal 10'6" height door?  
  Were these actually made so they would fit 'slight' (?) differences in height?
Done at different times ("evolving technology")?  Some other reason?

  And, for that matter, was there a significant difference between the Youngstown
doors and some other makers?

  Or was it all about the cost ... at a point in time?
                                                                                                      - Jim in the PNW