He first worked for Motown in 1959, and wrote arrangements for the Temptations, Stevie Wonder, and the Supremes among others. He later worked for the Stax label, working with leading musicians such as the Staple Singers, the Dramatics and Isaac Hayes. After arranging strings and horns on Hayes' album "Hot Buttered Soul", the pair worked together on "Shaft", and at the 14th Annual Grammy Awards in 1972 jointly won the award for Best Instrumental Arrangement for "Theme From "Shaft"". Allen also worked consistently with Detroit producer Don Davis at his United Sound Studios, providing arrangements for acts such as Johnnie Taylor and The Dells.