The block itself has nothing to do with the amount of horsepower the car makes, it has to do with the amont of hoserpower it can take. The Teksid block is desired for its toughness, not its performance.
The '01 Cobra's were quicker than the models before it because of its head/intake design and ECU tune. That's really all there is to it.
A lot of people think they need the Teksid block because of all the power they plan on making. I can't tell you how many people I've seen that have wasted the money going with this block, only to make between 300-600hp. For what they spent on the block, the could have covered the cost of a good performance part.
The rods and pistons in the early Cobra's are made of the same fragile material that the ones in the GT's are. They utilized rather weak hypereutectic pistons, and cracked cap powdered rods. Ok for horsepower levels in the 400hp range, but much beyond that they start living on borrowed time. The cranks are forged steel and will take all kinds of power, but if you ever plan on making any serious power with this engine, look into a set of forged steel H/I beam rods and some forged pistons that'll take the heat.
The number one formula that seems to do the trick for Cobra's is gears, high flow exhaust and intake mods topped off with an ECU tune. You can pick up a good 30-60hp this way and really turn your car into an animal....both on the street and at the track.