Listed in the .pdf, attached.
@Schurkey thanks for the .pdf.
I read something within that .pdf which said:
3. PG Starter Shimming
Many times an upgrade to a PG design eliminates the need for starter shims. However, due to variations in engine block machining, the replacement PG starter may still require shimming.
Why is this???
I have read this before, and I remember it being mentioned as an attribute of the PMGR ACDelco 337-1022 which I bought in 2012 for my L31 Suburban.