Grand Funk was originally Grand Funk Railroad which is taken from Grand TRUNK Railroad which was a RR line that went through Michigan (their home state) and Canada(?) and other places. Don’t know if they got in trouble for it, though. Feel free to fill in the holes.
This was kind of a sore point, as the cartoonists for the comic book, Los Bros Hernandez, actually had a band going called Love and Rockets when these British poseurs subsequently swiped the title. Los Bros didn’t have the kind of money needed to pursue this through the courts and grudgingly renamed their band “Nature Boy.”
Toad the Wet Sprocket was named for a throwaway joke band name from a Monty Python sketch. One of the Rolling Stones (Bill Wyman?) had a side project in the 80s, Willy and the Poor Boys, named for a fictional blues band in a Credence Clearwater Revival song, “Down on the Corner.” Buckcherry, of course, is a spoonerism for Chuck Berry.
An old name for the Grateful Dead (itself a Thomas Merton reference) was “Mother McCree’s Uptown Jug Champions.” I’m sure there’s a story behind that name, but I have no idea what it could be.
Amon Amarth’s last 3 albums have charted top 50 in the U.S, and top 10 in several European countries. Much smaller musical acts have been sued for fairly small things. So, I think it has nothing to due with popularity.
According to Wikipedia: R E O Speedwagon formed in 1967.
From the same source: REO Motor Car Company closed in 1975.