A-36A 42-83665 NX39502
This Mustang/Apache had a couple different appearances at the races of the 1940's. She first showed up as #15 "City of Lynchburg" then race #44 sponsored by "Essex Wire Corp." and finally in 1949 as race #2. The aircraft had a crash landing in 1947 and this picture must be during the 49 Cleveland or so. It ended up in storage in Council Bluffs IA and was acquired by the USAFM in 1971. A static restoration was completed in 73 and she has appeared at the USAFM as the "Margie H" ever since...
I guess it's another shot of 43-6007. I thought it might be Ken Everson's Essex Wire racer at first ... but under close inspection back when chuck Doyle had the Essex Wire airplane (42-83665, one could still make out the paint design from the racing days ... and I don't remember the diagonal stripe just behind the cockpit.
See page 73 of "Mustang: The Racing Thoroughbred" for a picture. Clearly NX39502, a A-model flown by James Hanon at Cleveland '49. Note the "Sohio" decal on the Mustang in the background of your photo--no doubt it's post-war Cleveland. Also look closely for the fuselage stripe and racing number 2 on the fuselage. The Mustang book also has a 1948 Cleveland photo of '39502 painted as the "Essex Wire Corp." special.