To get a 99-01 Cobra to get anywhere near 500-600 rwhp you will need to upgrade the internals, tranny, clutch, fuel system, get a blower.
A 99-01 could handle 430-450 rwhp with the stock internals and a good fuel system. Plus you have to be careful with the compression.
My buddy has an 04 with 644 at the tires. He has an upgraded fuel system and a KB with a 26 spline input shaft, Ram clutch, an IRS brace and a MAFia extender.
His car handles that power very well. Stock internals, but they are all forged.
My car is now over 500 rwhp(518) but before, I was at 490(see sig)with stock everything including injectors. I am about maxed out though before I get a BAP and 60#'ers.
My goal is 550 with the Eaton. I should get it with the Meth and lower pulley.