Back in 1988, before the Disneyland version opened, an article about the ride was featured in
an issue of Disney News magazine.
At one point in the article, it says this:
So it would seem that the plan was for Brer Roadrunner - this guy, right here...
View attachment 354015
...and who is ALSO placed in-between Brer Rabbit and Brer Terrapin and the Hitchhiking Alligator - to be the one singing the verse. I do not know why they changed it.
This roadrunner ALSO appears in the Walt Disney World version, where he instead asks the riders if he can come along to the Laughing Place...
View attachment 354017
As for this other question...
I always thought the Imagineers decided after the Disneyland version was built that they looked better with the top hats (and, to be honest, I think so too). That's just my theory, though.