What constitutes a groove?

[My70C10]

I have attached a pic of a saginaw 3 speed replacement transmission going into my son's 1970 C-10 stepside. I've found all the sites that talk about grooves on the input shaft. I'm trying to determine if this is wear on the front bearing retainer or are these markings the allusive grooves mentioned in other tranny id articles. No one has ever posted a pic of a one groove, 2 groove, 3 groove, etc. trans so I don't know what to look for.

Thanks.