Not sure if they make 'em for the Cobra, but Unitrax makes the best ones for the Viper. They're rated for applications exceeding 1000rwhp, but they cost around $1500 for the pair.(ouch)
DSS makes halfshafts. I think 1200 for stage 2, and 1600 for stage 5. Jay Knott(730+RWHP) runs the stage 5's, and he was the test car for DSS. I would really like to see another company step up to the plate, and make some for a little cheaper than 1200 or 1600.