In terms of vocals, I can think of 3 Beatles songs having very Beach-Boys-esque harmonies: Because, Sun King and Back In The USSR.
Stripped down "acapella" videos of these are linked below.
For compare-and-contrast fans...I have included three acapella Beach Boys tracks: Surfer Girl, In My Room and When I Grow Up to Be a Man.
I'm not making any point, one way or the other, here...merely serving up some food for thought and discussion...
Beatles acapella Because
Beatles acapella Sun King
Beatles acapella Back in the U.S.S.R.