125 shot should be fine with colder spark plugs, a bigger fuel pump, and an adjustable fuel pressure regulator. You can do this for $700 total.
However, you still won't beat him solidly with JUST a 125 shot. My GT coupe went 13.3 with a stock motor and transmission on a 125 shot with 4.10s, drag radials, exhaust, and weight reduction...with your heavier weight, 3.73s, and street tires you'd probably be more like high 13s.
Plus, the 125 on a stock AODE WILL destroy it eventually.
A 125 shot + a torque converter, shift kit, and tranny cooler will allow you not only to soundly beat the Cobra, it'll preserve the life of your AODE.