Is the casting# teh same between 69-72 and the 73-only?
They are the same spindles in fitment with the exception of the machining for the inner bearing and seal, the 73 has a larger journals.
So the machining would change the part#, but not the casting# (if they are indeed the same casting).
I looked at my spare spindles, 1 of 69-72 and 2 of 73, and there is no consistency of numbers, fonts, etc. 2 of my spindles of the opposite hand from yours have numbers cast in.
Best way to ID is to measure the bearing journal and compare vs the ID of the 2 inner bearings that were used in this era.