I picked up some Walden-Worcester oval drive sockets. There are some interesting variations on the 5 sockets. All are 6 point. The 77xx series are a smaller drive size than the 78xx series.
Oval drive on these measures roughly .465 x .550
7712 3/8" 1 threaded hole w/set screw
7716 7/16" w/2 holes-1 threaded w/set screw
7719 9/32" 1 threaded hole missing set screw
7720 5/8" 2 holes 1 threaded w/set screw
Oval drive on this measures roughly .505 x .610
7824 3/4" 2 holes-1 threaded w/set screw