To make a cobra
 

What would it take to make a 98 mustang gt to be exactly like a 98 mustang cobra. Like what kind of heads, gears, exhaust, etc. Do they have automatic trannys for cobras.

To be EXACT you're talking a real pain in the *** . Cobras have a different block, heads, crank, pistons, rods, timing chains, covers, intakes, shocks, struts, springs, bumpers, hoods, fog lights, headlights, radiators, some interior stuff, ect. and they all come with T45 5 speed manuals. The GTs and the Cobra are kissing cousins as far as design, but if you get down to the details, they are very different cars.

Its not at all practical to convert a GT to a 100% (less the builders) Cobra. If you want your GT to be faster (or much faster) then a Cobra, then that's a different story. But I wouldn't bother trying to convert.

The easiest way is to just trade your car in for one. I'm sure any dealer or private seller would be looking for more than $20K, depending on mileage. As 97snake already alluded to, there's too much expense and hassle to do it any other way.