I have a 1987 Hot Rod Automotive Series Shelby American guide and it has the original specs on all cobras:
Cobra 427(Street)
Engine: 428 CID Special Police Interceptor with engine modifications by Shelby American, compression ratio 10.0:1, 1-4V ford Carb(I think it is a holley built ford carb), HP 390@5200rpm; torque 475@3700rpm, mechanical lifters, milage 9-12mpg, premium fuel only.
Cobra 427(Some Street cars)
Engine: 427 CID 2-4V ford Carbs, HP 425advertised, mechanical lifters There was not as much tech info on this motor but they call it the NASCAR motor
Cobra 289(1964)
Engine: 289 CID HI-Performance Ford Fairlane V8, compression ratio 10.0:1, 1-4V ford Carb, HP 271@5800rpm; torque 269@4800rpm, mechanical lifters, premium fuel only.
Optional HP up to 370HP with Webbers
IMHO the big blocks are more for show. Yes they are fast and in most street applications faster than a small block. They create more heat that can make the car less enjoyable to actually drive. The FE motors are not the best in terms of reliability. The 429/460 is a more modern motor with more parts available for it. If you go the small block route I would stay away from strokers as that runs the cost up to the big block area and then you start stressing parts.
Remember a Cobra with a stock 225hp 5.0 will outrun almost any stock production car on the road. Cobras are about low weight and low center of gravity. Driving one is fun and will make you a simi-celebrity that people give thumbs up to unless you are Natalie Maines(in that case you do not need to drive an open car. I suggest a bullet proof Hummer with dark tinted windows)
