Add up boxes circulating top-notch features (6,5)

'features' is the definition.
The answer and definition can be both body parts as well as being plural nouns.
Maybe you can see an association between them that I don't see?

'add up boxes circulating top-notch' is the wordplay.
'add' becomes 'sum' (synonyms).
'up' says the letters should be written in reverse (in down clue: letters go upwards).
'boxes' indicates putting letters inside (the outside letters must 'box' inside letters in).
'circulating' indicates an anagram.
'sum' in reverse letter order is 'mus'.
'top'+'notch'='topnotch'
'topnotch' is an anagram of 'ttonchop'.
'mus' going around 'ttonchop' is 'MUTTON CHOPS'.

Can you help me to learn more?