"373" axle sales code 1965 Barracuda

Anybody know what rear end the number "373" on a 1965 Barracuda FS build sheet means. The number is under Axle" between "Engine" and "Tires". I know 374 means 3:23 and 372 means a 2:94, but I never have run across a code 373. Maybe a 8 3/4" heavy duty rear since the build date is early February 1965 and it is a 4 speed car.