So, I don't really know anything about how the Marine Corps organized itself IOTL. I take that IOTL the Marines took the first option of getting ready to fight the Soviets head-on? I recall the Marines having Abrams tanks, which are obviously not amphibious, the Marines certainly didn't absorb the 82nd Airborne, so they must not have taken the "we'll handle the rapid reaction" route, and presumably you're not starting an AH by describing how nothing differed from OTL, so...
There's no significant changes til the very end of the chapter.
If anything, I underplayed just how hopeless the Marine Corps was from 1972 to 1979. It was widely considered that amphibious warfare was obsolete against a modern enemy, and the other portion of the NSA of 1947 that gave the Marine Corps its mission was "and execute other duties as may be directed by the President." But this ability was severely curtailed by the War Powers Act after Vietnam. Besides, no one thought we would be fighting any wars besides World War 3. Small scale interventionism was effectively dead after Vietnam.
They kind of stumbled upon the mission defending Norway (later Jutland and Iceland as well, which is why they're there in
Red Storm Rising) by accident. Even though the Army was at 16 divisions by then they just didn't have the forces to do anything up there in the event of war. They were going to go all out in Germany, and so were the rest of NATO. So the Marine Corps was basic jumped up and shouted "Yippee! A Mission!"
What I didn't get into were the changes under the Carter Doctrine. After the Oil Crisis and the Iranian Revolution it was clear that the Persian Gulf was an area of vital national interest to the United States, and we would intervene militarily if needed. He created the Rapid Deployment Joint Task Force with a Marine General Commanding it, and the Army allocated light forces. It fit what both the light forces and Marine were looking for, a way to fight on the periphery and still have a major impact.
So it wasn't so much that the Marines were to fight the Soviets head-on. The Army would be doing that in the Fulda Gap, but that the Sovs may look to make inroads in strategically vital areas outside the main theater of operations. That's where the Marines expected to fight.
But all of those crazy ideas I alluded to were considered at one point- Marine Armor Divisions, Airborne Divisions, etc. They would have converted half of the Marine Corps to that format. It was ultimately rejected because it would create two separate tribes in an already small service. I believe those proposals also considered eliminating Marine Corps tactical air, which had been a key component to the Marines' identity since the World War.