Complex sentence: Following the sacking of Mick Roche (Billy Mac's replacement) in 1974, Fran O'Toole fronted the band, the group often being billed as Fran O'Toole and the Miami.
Split into simpler sentences: Following the sacking of Mick Roche (Billy Mac's replacement) in 1974, Fran O'Toole took over on the lead vocals. Thereafter, Fran O'Toole fronted the band, the group often being billed as Fran O'Toole and the Miami.