The manual has a typo, it's actually 1-3/4" long. Typo is in the parts list where it says 1-1/4", the correct size is in the text of the manual.
THe core of the power transformer is itself 1-1/4" thick. Then make allowance for the bell end cover, shoulder washers, lockwashers, chassis plate, and nuts - 1-1/2" is just not quite enough. Unfortunately 1-3/4" is quite a bit harder to find than 1-1/2" or 2".