Theme: Double, Double - but not Toil and Trouble. Two-word phrases; each word starts with the same two letters.
20A. Earnings before the government's cut: PRETAX PROFITS
38A. Words on a "No Trespassing" sign: PRIVATE PROPERTY
54A. Invention that revolutionized book production: PRINTING PRESS
53D. Ad agency guys responsible for 20-, 38- and 54-Across?: PR MEN. Men, because there are two PR's per entry.
Argyle here. Nice spanner. Didn't really need a reveal but it's a cute reveal so ok. Brock has become quite the Monday specialist.
1. British bloke: CHAP
5. Title for a fictional fox: BR'ER
9. Pancake syrup tree: MAPLE
14. Prefix for "six": HEXA
15. Coleridge's "The __ of the Ancient Mariner": RIME
16. Partners of pains: ACHEs
17. Many Manet works: OILS
18. Like a grand-scale fail: EPIC
19. __ Islander: small-state resident: RHODE
23. End in __: come out even: A TIE
24. French street: RUE, as in "The Murders in the Rue Morgue". The Rue Morgue is a fictional street in Paris.
25. Cops' orgs.: PDs. Police Departments
28. Fave pal, in 67-Across: BFF. (Best Friends Forever). 67-Across. Cellphone messages: TEXTS
31. German pastry: STRUDEL. Braided Apple Walnut Strudel
33. Question as to technique: HOW
34. New Haven collegian: YALIE
36. Cribbage piece: PEG
37. Gossip columnist Barrett: RONA
42. Rockers' sound machines: AMPs
43. Speck in la mer: ÎLE
44. Coloring cosmetic: ROUGE
45. Chessmen and board, e.g.: SET
46. Squeaky clean, as hospital supplies: STERILE
49. Alternative to grass seed: SOD
50. "No seats" initials: SRO. (Standing-room only)
51. Big __: trademark burger: MAC
52. Gunk: GOOP
60. First appearance: DEBUT
62. Promises at the altar: I DO's
63. __ Hari: MATA
64. Smidge: SKOSH
65. "Me neither": "NOR I"
66. Getting people out of harm's way, for short: EVAC. (Evacuation) Who's next?
68. Secluded valley: GLEN
69. __ of the woods: NECK. Area.
1. Lamb serving: CHOP
2. Will beneficiary: HEIR
3. Rod on which wheels turn: AXLE
4. Rotini or rigatoni: PASTA
5. Secession approved in a 2016 U.K. referendum: BREXIT. (portmanteau of "British" and "exit")
6. Jack the __: RIPPER
7. Arab leader: EMIR
8. Piccolo relative: RECORDER. Grace Slick on the recorder, gives the song a haunted sound.
9. Actress Hemingway: MARIEL. Don't look to close.
10. German eight: ACHT. More German.
11. Element in matches: PHOSPHORUS. Wiki article White phosphorus hasn't been used for regular matches for some time but you can still get "strike-anywhere" matches.
12. Conducted: LED
13. Language suffix: ESE
21. On the Caribbean: AT SEA
22. En __: on a hot streak, slangily: FUEGO. Spanish, 'on fire'. (Don't play with matches!)
26. "Stick around": "DON'T GO"
27. Influenced: SWAYED
28. Road that avoids the city center: BYPASS
29. Crop raiser: FARMER
30. Container with an attached cover: FLIPTOP BOX
32. Michigan's __ Peninsula: UPPER
35. Drips in a hosp.: IVs
37. Classic roadster: REO. Ransom Eli Olds
39. Giant: TITAN
40. Putting in office: ELECTING
41. Surg. holding area: PRE-OP
46. Workers with anvils: SMITHS.
Under a spreading chestnut-tree
The village smithy stands ...
Thanks, thanks to thee, my worthy friend,
For the lesson thou hast taught!
Thus at the flaming forge of life
Our fortunes must be wrought;
Thus on its sounding anvil shaped
Each burning deed and thought.
47. Pay no mind: IGNORE
48. Begins a computer session: LOGS IN
55. Oxidation damage: RUST
56. Beloved star: IDOL
57. Roof gutter locale: EAVE
58. Like short, clipped notes, in mus.: STAC. (staccato)
59. Burlap container: SACK
60. Va. summer hours: DST. [Eastern](Daylight Saving Time)
61. __ out a living: EKE. Eek! Time to put this to bed.