Across:
   1. Arrangement to see about cut for B5 (7)
   5. see 32
  11. Some spinning spinning drink (3)
  12. Windows, say, in backing of T5 (2)
  14. see 57 down
  15. Obliterated early leader in slam-dunk (5)
  16,43. Prog band ply kind of novelty (4 5)
  17. Note: extension given by this (3)
  19. Light metal in backing of T6 (2)
  20,6dn,63. "Star Spangled Banner" is about vitamin B2 (2 3 4)
  22. Loud one for T4 (2)
  23. Badly dyed as swirl (4)
  25. see 39
  27. Brief education of Sullivan? (2)
  29. see 46
  31. Second round for T5 (2)
  32,5. Support in "Mother" with 49 down for B4 (5 6)
  34. see 56
  36. On/off rejection? (2)
  38. Urban West Coast sound for T6 (2)
  39,49,25. Make pesto sauce A1 (5 2 2)
  40. The Spanish American railway? (2)
  41. French... and alien! (2)
  42. Chinese Greek character (3)
  43. see 16
  45. Computers etc. in backing of T7 (2)
  46,24dn,39dn,18dn,46,60. A plus B put together by 16 43: problem with exposed rear? (3 4 4 2 3 4)
  46,30dn,29,51dn,46,10dn. True heroin ("one taken by heron") gets soldiers, along with cooler number "n" for A5 (3 5 3 2 3 3)
  48. Some weight in album! (2)
  49. see 39
  50. Links on site crashed (4)
  52. Record easy bits for T2 (2)
  54. Poem among seconds of Kipling offerings (2)
  56,46,34. Unthrone unhinged A3 (2 3 3)
  58. How old? About, say, one? (3)
  60. see 46
  62. Suddenly pulls last of heavily armoured vehicles, losing 49 down (5)
  63. see 20
  64. Hesitation in backing of T2 (2)
  65. A party kerfuffle (3)
  67. see 57 down
  68. Ate herb cooked for A2 (7)
Down:
   2. Empire overrun by Incas... as such I'm unusually restricted (5)
   3. Chilled and played dice (4)
   4. Warning America "Against Interpretation", who thus ends up being influential philosopher? (6)
   6. see 20 across
   7. I'm back for T3 (2)
   8. Fruity use? (5)
   9. One out in 49 down (3)
  10. see 46 across
  13. Isle with cooler cycle (4)
  18. see 46 across
  19. Modern times to ancient Roman (2)
  21. Sound of spot, or spot beyond sound? (3)
  24. see 46 across
  25. One in my embrace is B1 (5)
  26. Enjoying gift in crab legs (4)
  28. Spinning CD is included, or vinyl record perhaps (4)
  30. see 46 across
  33. For proportion invested into it, a reasonable return! (5)
  35. This means nothing to a computer programmer! (4)
  37. Parents sold out (4)
  39. see 46 across
  44. Belt little bird's wings off (3)
  47. In computer, a serious error may be removed with this (6)
  49. Some sheet I measured as A4 (4)
  50. Following chord structures to new and lengthy introductions (5)
  51. see 46 across
  53. Notes that strike a chord with B or C for instance (2)
  55. Tissue is fresh but has changed hands (5)
  57,67ac,62dn,14ac. Lulu, Yoyo, Rick A... one amazing line-up for B3 (3 6 3 4)
  59. Exploding mountain upset initial investment (4)
  61. Bring up oscilloscope for monster (3)
  62. see 57
  66. Party with T1 and T8! (2)