Cobb and Musial hit five home runs in two consecutive games in the same park and Colbert watched Musial.

Ty Cobb did it in consecutive days in 1925. Stan Musial did in a doubleheader in 1954.  But they both did it in the same ball park even though that park had a different name.

http://www.retrosheet.org/boxesetc/S/PK_STL07.htm

Originally known as Sportsman's Park III
Name changed to Busch Stadium I in 1953

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https://en.wikipedia.org/wiki/Sportsman's_Park

From 1920–1953, Sportsman's Park was the home field of both the St. Louis Browns of the American League, and the St. Louis Cardinals of the National League, after which the Browns departed to become the modern-day Baltimore Orioles. The physical street address was 2911 North Grand Boulevard. This ballpark (by then known as Busch Stadium, but still commonly called Sportsman's Park) ...

Field size	Left Field: 351 feet (107 m) Left-Center: 379 feet (115 m) Deepest corner (just left of dead center): 426 feet (129 m) Deepest corner (just right of dead center): 422 feet (128 m) Right-Center: 354 feet (107 m) Right Field: 310 feet (94 m) Backstop: 68 feet (20 m)

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A lefty batter pulling to right field had a pretty easy shot for a home run.  You can read about Cobb's performance in this post:

Ty Cobb hit five home runs in two consecutive games. Does that prove he could have hit like Babe Ruth?  Thursday, July 2, 2015

Musial's game one against the New York Giants: http://www.baseball-reference.com/boxes/SLN/SLN195405021.shtml

http://sabr.org/bioproj/person/2142e2e5

Musial's greatest single day on the baseball field came on May 2, 1954, in a doubleheader in St. Louis against the eventual pennant and World Series winners, the New York Giants. He went 4-for-4 in the first game with three homers, including the game-winner, a three-run shot off Jim Hearn, and 2-for-4 in the second game (a Cardinals loss) with two more homers. Coincidentally, witnessing the five homers was an eight-year-old named Nate Colbert, who as a San Diego Padre would equal Stan's record of five home runs in a doubleheader, in Atlanta on August 1, 1972.
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https://en.wikipedia.org/wiki/Nate_Colbert

Nathan Colbert Jr. (born April 9, 1946 in St. Louis, Missouri) ...

Signed by his hometown St. Louis Cardinals as an amateur free agent in 1964 ...

Colbert's best day in the majors was August 1, 1972, when he slammed 5 home runs - one of two players to have done so, Stan Musial being the other in 1954 - and drove in 13 runs in a doubleheader, breaking the record of 11 runs batted in. Coincidentally, a young Nate had attended the game where Stan originally set the HR record. This helped the Padres sweep the Atlanta Braves, 9-0 and 11-7.
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Like Cobb, Colbert's team won both games while Musial's split.  Colbert was unlike Cobb and Musial:
- batted righty
- hit two homers in the first game, then three in the second; they hit 3, then 2
- not in the Hall of Fame.

Colbert's game one against the Braves in Atlanta Stadium (the launching pad): http://www.baseball-reference.com/boxes/ATL/ATL197208011.shtml

I could not find anything to support the story that Colbert attended Musial's doubleheader.  It's obviously possible; Colbert would have been eight years old and was born in St. Louis.  It's also possible that Musial's accomplishment so impressed Colbert that he later imagined that he had actually been there.

Reggie Jackson Born: May 18, 1946 in Abington, PA

Abington township is just north of Philadelphia.  Hershey, PA is to the west, just east of Harrisburg, where in 1962 Wilt Chamberlain scored 100 points against the New York Knicks.  Reggie Jackson claims to have attended that game.

http://m.mlb.com/news/article/26952736/

"I was there," Reggie says with pride. "I was there that night. One hundred. I saw it. How does one man score 100 points in one game?" ...

Reggie, his father and his brother were there

"My father had a dry-cleaning business in Lower Marion," Reggie said. "We cleaned the clothes of rich people. He had to make deliveries about 20 miles from Hershey, so he took us. We saw something very few people saw.

Attendance that night in an antiquated arena, including the three Jacksons, was merely 4,124. Few New York papers covered the game. The wire services sent stringers. No visual record exists, and most of the audio is from the fourth quarter only. But Reggie can speak of Wilt's night.
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I'm inclined to think that Reggie attended Wilt's 100 point game.  Our fascination with these super achievements is very positive.