Formula for letters and reverse order

I need a way to look at column G, count how many of the same number, then take total number and convert it to letter. add that letter to the top of the series, and run it down. Finding it really hard to describe, so i'm sorry for any confusion. Added in manual cells to show what the result should look like.
Column B,C,D is the old system, and i'm trying to convert to the new system in column F,G and H