Model on the radio welcoming line in The Palace (6)
I believe the answer is:
castle
'the palace' is the definition.
('castle' can be a synonym of 'palace')
'model on the radio welcoming line in' is the wordplay.
'model' becomes 't' (Ford Model T car).
'on the radio' becomes 'case' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'welcoming' is an insertion indicator (in sense of 'inviting in').
'line' becomes 'l'.
'in' means one lot of letters goes inside another.
'case' going around 'l' is 'casle'.
't' placed into 'casle' is 'CASTLE'.
Can you help me to learn more?
(Other definitions for castle that I've seen before include "Fort" , "secure place" , "Chateau" , "Big building" , "a piece in the corner" .)