Complex sentence: Morton's first theatrical success had been to launch and sustain the careers of the renowned magicians Maskelyne and Cooke at the Egyptian Hall and was also currently managing the thousand-seater New Cross Public Hall.
Split into simpler sentences: Morton's first theatrical success had been to launch and sustain the careers of the renowned magicians Maskelyne and Cooke at the Egyptian Hall. Morton was currently managing the thousand-seater New Cross Public Hall.