Guy with gangster stealing one of the crown jewels? (7)

'crown jewels?' is the definition.
The definition and answer can be both body parts as well as being singular nouns.
Perhaps they are linked in a way I don't understand?

'guy with gangster stealing one' is the wordplay.
'guy' becomes 'gent' (I've seen this in another clue).
'with' is a charade indicator (letters next to each other).
'gangster' becomes 'al' (Al Capone).
'stealing' means one lot of letters goes inside another.
'one' becomes 'i' (Roman numeral).
'gent'+'al'='gental'
'gental' going around 'i' is 'GENITAL'.

'of the' is the link.

Can you help me to learn more?