I know that when US domestic carriers first started operating widebodies in the early 1970s they operated with much more spacious configuration that what later became the norm. For example:

747 coach configuration was 8-9 seats across, instead of 10 across
DC-10 and L-1011 coach configuration was typically 8 instead of 9 seats across.

When was this changed?

TranStar

Almost all early 747 and DC-10/L1011 operators had replaced the original 9-abreast economy class seating on 747s and 8-abreast (2-4-2) on DC-10s and L1011s by the late 1970s. By 1980 I think there were very few aircraft operating with the original more spacious configurations.

Many aircraft were being delivered with the denser seating by about 1974 or 1975. I remember a BA trip ORD-LHR-ORD on BA 747-100s in March 1974. The outbound flight had the original 9-abreast seating and the return flight had the new 10-abreast seats. So BA's 9-abreast 747 layout only lasted about 4 years.

Ironically, BA's L1011-1s used on intra-Europe flights had very tight 10-abreast (3-4-3) seating in Y class while the same aicraft type used by US carriers and several others at the time had the spacious 8-abreast layout.

When were the passenger louges taken out?

Quoting Viscount724 (Reply 1): Almost all early 747 and DC-10/L1011 operators had replaced the original 9-abreast economy class seating on 747s and 8-abreast (2-4-2) on DC-10s and L1011s by the late 1970s.

The L-1011 original seating arrangement was 2-4-2 with coat storage between the center seats, not 9-abreast. The first 10-abreast seating arrangement was installed on the 400 passenger Court Line TriStars (s/n 1024 and 1032). These were delivered in early 1973.

Quoting 474218 (Reply 3): Quoting Viscount724 (Reply 1): Almost all early 747 and DC-10/L1011 operators had replaced the original 9-abreast economy class seating on 747s and 8-abreast (2-4-2) on DC-10s and L1011s by the late 1970s. The L-1011 original seating arrangement was 2-4-2 with coat storage between the center seats, not 9-abreast.

I didn't say the original L1011 arrangement was 9-abreast. You must have misread my posting you are referring to above.

Most lounges went out by 74. Some airlines like
National never had them. Continental brought lounges back in '78/79.