Theme: Sing, Sing, Sing! - Three musical numbers from a 1957 Broadway production.
20. Julie Andrews' "The Sound of Music" role: MARIA VON TRAPP
25. Jimmy Fallon hosts it: THE TONIGHT SHOW
43. Avengers member with a patriotic shield: CAPTAIN AMERICA
50. 9/26/1957 Broadway debut featuring the consecutive songs found at the start of 20-Across, the middle of 25-Across and the end of 43-Across: WEST SIDE STORY
Argyle here. The theme was lost on me until I read the full reveal. Clever.
1. Sales pitch: SPIEL
6. Outback birds: EMUs
10. Sunup: DAWN
14. Café lure: AROMA
15. Clickable webpage word: LINK
16. Home to billions: ASIA
17. Grass shortener: MOWER
18. Apart from that: ELSE
19. Slightly wet: DAMP
23. Risk, e.g.: GAME
24. Healthful berry: ACAI
31. "Homeland" spy org.: CIA. (Central Intelligence Agency) Homeland is a TV series on Showtime and is in its sixth season.
32. Taxi: CAB
33. Nebraska city: OMAHA
34. "Apocalypse Now" setting, familiarly: NAM
35. Gathering for fans of graphic novels, anime, etc.: COMICON. (comic book convention or comic-con)
38. Delivery vehicle: VAN
39. Painting need: BRUSH
41. Microwave: ZAP
42. Valuable rock: ORE
48. Tolstoy's Karenina: ANNA. 864 pages; too late for a summer read.
49. Dutch cheese: EDAM
55. With 50-Down, tightrope walker's place: HIGH. 50-Down. See 55-Across: WIRE
56. Oscar winner Kazan: ELIA. Best Director—"Gentleman's Agreement"(1948) and "On the Waterfront"(1955) Also, Academy Honorary Award—Lifetime Achievement(1999)
57. Aquafina rival: EVIAN. Bottled water products; Aquafina - Pepsi, EVIAN - Danone(French)
59. Craving: URGE
60. Accelerates, with "up": REVS
61. Foolish: DIPPY
62. Military meal: MESS. 63. Cafeteria carrier: TRAY. Good pairing.
64. V-formation fliers: GEESE. They are starting to form up now.
1. "Casablanca" pianist: SAM
2. Formal school dance: PROM
3. Corn Belt state: IOWA
4. Rise into view: EMERGE
5. Cattleman's rope: LARIAT
6. Late morning hr.: ELEVEN AM
7. Venus de __: MILO
8. Disentangle: UNSNAG
9. Quick drawing: SKETCH
10. Arp's art movement: DADAISM. Dada was not so much a style of art like Cubism or Fauvism; it was more a protest movement with an anti-establishment manifesto.
11. Right away, in a memo: ASAP. (as soon as possible)
12. Namby-pamby person: WIMP
13. Midday snooze: NAP
21. Gas brand that had a torch in its logo: AMOCO
22. Florida's Boca __: RATON
25. Pageant winner's crown: TIARA
26. Exaggerate, as a stage role: HAM UP
27. Spanish island in the Mediterranean: IBIZA
28. Devastation that's wreaked: HAVOC
29. Scarlett of Tara: O'HARA. Gone with the Wind
30. Decrease in intensity: WANE
31. "Closing Bell" channel: CNBC. (Originally, the Consumer News and Business Channel.) The show is named after the bell that is rung to signify the end of a trading session.
35. Repetitive shout at a protest: CHANT
36. Required little effort: CAME EASY
37. Newspaper opinion pieces: OP ED's
40. Secret supplies: STASHES
44. Add to text, as a missing letter: INSERT
45. Carpenter, at times: NAILER
46. Suitable for all ages, filmwise: RATED G
47. Apple software for creating videos: iMOVIE
51. Omelet ingredients: EGGS. Gotta break 'em to make an omelet.
52. Prima donna: DIVA
53. Ready for picking: RIPE
54. Toy dog's barks: YAPS
55. Play a kazoo: HUM
58. TV's "Science Guy": NYE