I went into training mode and went through every character and tried to find what normals gatlinged into their overhead normals. Of course this doesn't account for things like Ragna's gauntlet hades or lambda's TKed crescent or Carl's various shennanigans, but i figured it'd help people learn to block overheads if they knew what attacks might come before it.
Character (Overhead): attacks that go into the overhead
Ragna (6B): 5A, 2A, 6A, 2B
Jin (6A): 5A, 2A
Noel (6B): 5A, 2A, 6A, 5B
Litchi (6A): [m] 5A, 2A, 5B, 2B [e] 5A, 2A, 5B
Litchi (4D): [m] 5A, 2A, 5B, 2B, 5C, 2C
Bang (6B): 5A, 5C
Bang (5C): 5A, 2A, 5B
Lambda (4B): 5A, 2A, 6A, 5B, 2B, 6B, 5C
Rachel (4B): 5A, 2A, 6A, 5B, 2B
Hazama (6A): 5A, 2A, 5B, 2B
Tsubaki (6A): 5A, 2A, 5B(1, 2), 2B(1)
Hakumen (6B): 5A, 6A
Mu (6B): 5A, 2A, 6A, 5B
Arakune (6A): 5A, 2A
Arakune (6C): 5A, 2A, 5B, 5C
Taokaka (6B): 5A, 2A, 6A, 5B
Tager (6B): 5A, 6A, 5B, 5C
Tager (6C): 5A, 6A, 5B, 6B, 5C
Makoto (6B): 5A, 2A, 6A, 5C (1, 2)
Valkenhayn (6C): 5A, 5B, 5C, 2C
Carl (6C): 5A, 6B
let me know if i missed anything or if there's typos etc.