I've either written or am in the process of writing outlines for 14 of those names mentioned. Funny, I'd wager most people don't know that Peter Boyle could sing. Ditto Chevy Chase, who sang back-up for Carly Simon when she appeared on SNL.
I've only heard Peter Boyle sing once, on the SNL episode he hosted, and was surprised at what a wonderful voice he had!
I knew Chevy was a singer. In the 1960s, he was in various rock groups. Some of his bandmates over the years included members of Steely Dan and Christopher Guest.
The only group Chevy was in to hit it "big" was as keyboardist in a group called Chameleon Church. They actually released an album around 1968/69 on the MGM label.
In the early 1970s, he was part of the off-Broadway revue,
National Lampoon's Lemmings; the second act was a parody of the Woodstock festival, and Chevy (as well as other members of the cast, including Guest and John Belushi) played and sang back-up on many of the songs. Chevy even had a solo spot to himself, singing a John Denver parody called "Colorado."
I think Elliott Gould would have made a fantastic TMS host.
Perhaps Orson Welles, as well?