I had not heard of the Celts using this term; i assumed it was something from the Greco-Roman sphere only.
According to wiktionary Rammaz means strong (only coming to mean ram in proto-west germanic); now Bukaz does mean buck already so it is kind of plausible.
Maybe something like
Hand ram: Bagmawaldōz (beam wielders),Gataslahanōz (gate smashers)
Covered ram: Rammabukkaz
That could work.
Or something with those verbs?
https://en.wiktionary.org/wiki/Reconstruction:Proto-Germanic/wihslōną
https://en.wiktionary.org/wiki/Reconstruction:Proto-Germanic/saljaną
Also the axeman champion is called Slōgijanōz, maybe could be renamed to Slōgijanaz (my understanding is -az is singular and -ōz is plural).