Complex sentence: Approaching various charitable foundations, from 1955 Wheeler also secured funding from both the Pilgrim Trust and the Nuffield Foundation, and in 1957 then secured additional funding from the Rockefeller Foundation.
Split into simpler sentences: Approaching various charitable foundations, he secured funding from both the Pilgrim Trust and the Nuffield Foundation, which began in 1955. In 1957, he then secured additional funding from the Rockefeller Foundation.