A full treatment for all those interior parts (3,5)
I believe the answer is:
the works
'parts' is the definition.
The answer and definition can be both acts as well as being plural nouns.
Maybe they are linked in a way I don't understand?
'a full treatment for all those interior' is the wordplay.
'a full treatment' becomes 'works' (synonyms).
'for' is a charade indicator (letters next to each other) (I've seen this in other clues).
'all' becomes 't' (I can't explain this - if you can you should believe this answer much more).
'those' becomes 'them'.
'interior' indicates the central letters.
The central letters of 'them' are 'he'.
't'+'he'='the'
'works' put after 'the' is 'THE WORKS'.
Can you help me to learn more?
(Other definitions for the works that I've seen before include "plant?" , "(Give it) everything" , "factory?" , "Comprehensive treatment" .)