Fans of the Rutles and Rockpile, are you familiar with a band called Fatso?

Yeah, I remember that booklet but I don't have my copy handy. Never had the Rutland Weekend Songbook though.

It's mostly Eric Idle being pretty funny with a bunch of Innes songs. There are two Rutles tracks on that album which are not available anywhere else as far as I'm aware. A version of I Must Be In Love done with huge crowd noises a la Shea Stadium and a song called The Children of Rock'n'Roll which is later inserted into Good Times Roll.

What about George Harrison singing his Pirate Song?

Sadly not on the album though there are at least three other songs with nautical themes. In fact now I think about it "Song O' The Insurance Men" (a sea shanty about insurance) rather strangely seems to foreshadow the Crimson Permanent Assurance part of Monty Python's Meaning of Life.

BTW that song you posted at the top of the thread is on Neil Innes' album Taking Off with roughly the same crew.

Seems like the bass player in this band has the same name as a different guy, the Delia Derbyshire collaborator, BBC Radiophonic Workshop stalwart and Dr. Who composer Brian Hodgson.

https://www.youtube.com/watch?v=Ip-ZL4xI5zs