The Corvette and Viper do not have the power to weight ratio of a Cobra. Both have only about 400 hp. For a power to weight comparison, go to the following:
http://performanceunlimited.com/supe...eleration.html
With either a stroked SB or a BB, your problem will be hooking up, not torque or hp. You can easily get either with 500 or more torque and hp. What you will not have is all the modern ABS, magnetic shocks, active suspension, etc. of the modern car. You will have to be a much better driver or the Cobra will bite and kill you. It is a driver's car that will fault you on virtually every mistake that you make. With lots of torque and hp, it will be unforgiving.
The original Cobras could go 0-100-0 in 12 flat. The modern Cobra can do even better. You will have plenty of "snap" with either engine. The SB has the advantage normally of better weight distribution and ease of accessbility (the empty look has advantages). If your chief goal is to impress others on the street and when you park with the hood up, get a BB. It is pure macho. If you want better handling and curve road performance, get a SB.