The Incredible Upsetters were John Davidson, His brother ( Name unknown right now), Gene Armstrong, Waudell Hinton, Rex Robertson. All of whom have passed. Here is a link to a bio of John Davidson. He says the record label was Equador but he meant the bands name was Equadors. They never gigged under that name that I can see. One of the song writers on the Equadors was R Robertson (Rex).
http://www.gtcbms.org/adopted/jdickerson.html
The attached clippings come from the Call and Post. They had Rex Robinson as the former lead for the Upsetters, but had his name spelled wrong. Also Rex was the the First Husband of Kim Tolliver and died in a car crash in 1969. I am currently trying to get with some family members of the group to verify the history of the group. Also attached is a Ad from the C&P proclaiming them TAMALA (SIC) recording stars. All the clues fit together.... Matbe this is Rex singing lead and he did not sing any of the leads on the Incredible Upsetters EP.
Rex Robinson Upsetters 1967(3).pdf