HOUSTON ... WE HAVE A PROBLEM
It seems the 1955-1957 BIRD does take spacer(s) (QTY 3) . It is described in the MPC as 354193-S FLAT WASHER 13/32". Usually, that measurement is of the cap screw shank size but in this case must be the spacer thickness.
So that is how ENGINEERING designed the mounting and spacing for pulley alignment (
in addition to dedicated mounting brackets).
Below is ILL -
Parts Source -
https://www.npdlink.com/1955-1957-th...ering-brackets
NOTE - There are three of these spacers used on the BIRD PS install. Look @ ILL closely in prevous posts on this thread.