[cobraguy]

I like them both. Horsepower wise I would rate them as equal or maybe even give the edge to the 428 if the same amount of money is spent on both engines. Here's my logic.
A stock balanced and blueprinted 427 side oiler can set you back about 15 big ones or more. This engine will produce about 425HP and about the same or slightly more torque. If you stroke it by putting a 428 cast crank in it the 427 now becomes more like a 428 because that high reving durability has been reduced by replacing the forged crank. Why spend the money for the high nickel content block and cross bolted mains when the engine now is only good to 6,000rpm. A 428CJ block with thicker main bearing webs and caps is plenty strong enough.

For $15,000 on a 428 you can have a roller cam and rockers, weber 48 IDA's, Edelbrock aluminum heads ported and polished, Eagle rods, MSD ignition, billet distributor and a host of other goodies. With the above the 428 will probably produce more horsepower and torque than a stock 427 side oiler for the same money. If you intend to show the car nothing I mean nothing can top the look of an FE with a Weber setup. All of a sudden people aren't crawling under your car to see if it has cross bolted mains. As the Rock would say IT DOESN'T MATTER.

Point of interest more original 427 Cobra's came with 428's than with 427's. It is just as correct and original. If someone asks you if it's a 427 you can truthfully say yes as the 428 actually is closer to displacing 427ci than the side oiler. But most people ask if it's a side oiler and if it's important to you to be able to say yes then put one in. Either way they're both great engines and belong in a big block car.