Across:
   4. As part of notifying... ? (3)
   7. Boundary Commission essentially turned, with leaders of delegation eventually leaving 5 newly enraged (8)
   8. Engaged in street violence in prelude to Iranian revolution (6)
  10. Beat poet... real crazy, dropping ecstasy everywhere (6)
  11. Oddly, canniest one left out (as it emerges) (7)
  12. One established by 20 5 26 could be a test (4 5)
  14. Nasty slur after last of 5 plays 5 game (5)
  16. Beginnings of entente as French world farewell British gunners who opposed the 5 12 (5 2 6)
  19,23dn,2dn. Dail leader keenly taking a little look, then getting badly rogered as P.M. (5 5 6)
  21. Too choppy at sea in reproduction (9)
  24. Confuses counsel, bragging about housing (7)
  26. see 20 down
  27. A sorry arrangement that Catholics might cling to (6)
  28. They open out for new arrival (8)
  29. Executed sound horse? (3)
Down:
   1. Conflict's rage dies out (8)
   2. see 19 across
   3. Weight of daily grind taking terrible tolls in pit (9)
   4. see 25
   5. see 20
   6. Burmese lure Mohammedans back, offering what the 5 sought (4 4)
   9. Praise next Olympic hosts (5)
  13. Use some opiate & ether for dentist's business (5)
  15. Patriot in disturbance which split the country (9)
  17. Amazing diorama including northern highway (4 4)
  18. Cut off in Vietnam, put at ease (8)
  20,5,26ac. Deal struck in 1921 by 19 23 2 and 16's men is broken... he's a lying traitor! (5-5 6)
  22. Verbal promises of money for those in the republic (6)
  23. see 19 across
  25,4. A Finnegan is stirred when GAA kicked out of 5 party (4 4)