It's understandable you feel "trouble". The senence is indeed a bit ungrammatical (unlike 大ビーカー one, this sentence makes enough sense, though). How about this? Isn't it easier to understand, maybe?
リドルが、小さい時の友達の、ほとんど記憶のかなたに行ってしまった名前のような気さえした。
In the above sentence, 小さい時の友達の modifies 名前, so the meaning is more clear. The reason the meaning of the original sentence is unclear would be, I think, that リドル refers to a person in the former clause リドルが小さい時の友達(だ), whereas リドル is just a name in the latter clause ほとんど記憶のかなたに行 ってしまった名前のよう(だ). They are the same リドル, but what they express are actually different.