From: Somerset, U.K.
Interesting conundrum, but hard to say without a detailed understanding of how a range of factors might have interacted, e.g. officer corps politics, genuine considerations of merit and the "Buggins' turn" basis on which a number of IJN appointments were made.
I rejected Inoue Shigeyoshi for the appointment on the ground that he was too much of an iconoclast to be acceptable. I dismissed Ozawa Jisaburo on the ground that in 1939 he still a wee bit too junior. Both, however, are probably 'air-minded' enough to fill the bill.
Then you get the problem that many officers of the necessary seniority are too much in one camp or the other. Tsukahara Nishizo lacks the battle fleet experience. Conversely, Takasu Shiro, Kondo Nobutake, Hosogaya Boshiro and Koga Mineichi are too heavily imbued with a gun club outlook. Likewise Nagumo Chuichi, who in 1939 has yet to hold an air-related appointment.
So my choice is an admiral who doesn't figure prominently in histories of the Pacific War: V. Adm Katagiri Eikichi. He's a contemporary of Koga in Etajima's 34th class, elevated to Vice Admiral December 1937, at which time he takes command of the 3rd Sentai. The late 20's/early 30's sees him successively in command of Oi, Aoba and Haruna, so he has relevant gunship command experience. However, in November 1934 his career path takes an aeronautical turn, as he serves spells first as commander of 2 Koku Sentai, then as CO of Kasumigaura Kaigun Kokutai. In actuality he went to 4th Fleet as its commander in November 1939, but for your purposes an appointment to CinC Rengo Kantai at that time doesn't seem too outlandish.