Hi Rodney.
I would not use this method for a second grade reader. I would borrow the method used for labeled chemistry arrows shown in Section 3.1.2.a of that code book. It’s more graphic and follows print layout so a sighted helper is more likely to understand the braille.
See the attached brf file which illustrates this nice layout. Be sure to insert a blank line before *and after these constructions.
I also suggest using the general omission symbol for the omissions above the arrows. You can explain this layout and the substitution in the teacher notes that accompany your transcription.
Lindy