West Side gang returning note for high fliers (3,3)
I believe the answer is:
jet set
'high fliers' is the definition.
(I've seen this before)
'west side gang returning note' is the wordplay.
'west side gang' becomes 'jets' (I can't explain this - if you can you should give a lot more credence to this answer).
'returning' is a reversal indicator.
'note' becomes 'te' (musical note).
'te' back-to-front is 'et'.
'jets'+'et'='JET-SET'
'for' is the link.
Can you help me to learn more?
(Other definitions for jet set that I've seen before include "High fliers" , "Rich group of travellers" , "Rich and fashionable group who travel a lot" , "Fast-living group" , "Elite travellers" .)