David,
Toomey and Flynn already had a relationship by the time Alison contacted Flynn to partner up on projects in 1922. Flynn was a partner in two companies, the design company William S. Flynn, Golf Architect (he was the only designer) and Toomey and Flynn, Contracting Engineers. Toomey (there are no photographs that exist of him and next to nothing is known of him) was the firm engineer and handled the business administration. Toomey was 12 years older than Flynn and died in 1933. Near his death, Toomey told Flynn that he would now have to do all the drinking for the firm.
Flynn must have worked with Alison at Pine Valley on the construction of the alternate 9th green, an Alison design. Flynn later constructed Burning Tree (1924) according to Alison's specifications. We don't know how the partnership was presented to Flynn. We do know that Wilson, Piper and Oakley all suggested he not go into partnership with Alison, that he had great things in store on his own.