Just checked 'Spitfire, The History' by Morgan and Shacklady. Meredith himself made suggestions for altering the radiator on the Spitfire, and those suggestions were used in the Type 300 which became the Spitfire Mk I. Trials were done at the Farnborough wind tunnel on 1/4 scale models. Meredith also suggested different exhaust stubs, and a relocation of the carb intake, both suggestions were used.
Interestingly, the last fighter design that Reginald Mitchell worked on was the Type 312, which was a 4 cannon fighter with a nose postion ventral radiator.