[Stentor]

Mark,

First, congratulations on your decision to get an SPF. They are great cars. I also interacted with Eric (and the folks at Dynamic) when I was considering an SPF. He seems to be a stand-up guy.

Your choice in engine all boils down to personal preference. You will get ten different opinions/points of view from ten different people (there are clearly different camps you'll find on this site when it comes to small block vs. big block).

The 460-based 557 is going to be a bit heavier than the Windsor-based 427 (which at the end of the day, isn't typically a big deal for most people, unless you are going to be doing road racing).

However, the 557 is (on average) likely to produce more torque and hp at lower RPMs. A bored/stroked 460-based engine can be built to be very streetable (e.g., idles/runs fine at lower RPM, suitable for driving on the street in a 4-speed, 2600-pound car). You just need to clearly define for Eric (or whoever your engine builder is) what your objectives for the car are (e.g., primarily street driving, drag racing, road racing).

On the flip side, the 427W motor is very popular in its own right. Typically, this engine is going to be lighter (especially the aluminum block option), and you will get better gas mileage (Although, who really buys/builds a Cobra for gas mileage?).

At the end of the day, the 557 and the 427W are both fine motors.
It's all about your personal preferences, your objectives for the car, and the budget you have for your engine.

Good luck,

Kevin