The gist is rather a pipeline of Unix commands with no bash necessarily involved. Here it is in shellcheck-compliant 100% bash:

    #!/usr/bin/env bash
    shopt -s nocasematch
    while read -r word; do
        if [[ $word =~ ^[abcdefoi]{6,6}$ ]]; then
            word=${word//o/0}
            word=${word//i/1}
            word=${word^^}
            printf '#%s\n' "$word"
        fi
    done < /usr/share/dict/words

This could be collapsed to one line with semicolons. On the macOS 12.6 dictionary I get 59 words.

Edit: and in sed which someone just asked me for elsewhere:

    sed -n -e '
    /^[abcdefoi]\{6,6\}$/I {
    s/o/0/g;
    s/i/1/g;
    s/^/#/;
    y/abcdef/ABCDEF/;
    p;}' < /usr/share/dict/words