Don't know why you'd want to put a Viper engine into a Cobra, why not just buy a Viper? But as has been noted, it's your car, your dream, your vision.
Someone else has an even more bastardized vision, putting a Viper intake on an FE:
At least you wouldn't have to worry about mounts and headers and such, and it would definitely be unique (even more unique than a Viper engine in a Cobra which from the sounds of things has been done to death
)