[Cougar]

Rick, I have to disagree with your statement about torque... just a little. Of my 2 cars, I much prefer running my higher horsepower, higher rpm 347 motor over the mild but very torquey 392. The low rpm abundance of torque in the 392 just can't effectively be put to the ground in these light cars with street tires, but the high revs and strong upper end of my 347 is always amusing.
Matt, where is the battery in the SPF cars? If it is in the rear, like the FFRs, then there may be another pro to the aluminum. Go with an aluminum block, and move the battery to the front and you have shaved a significant amount of weight and better balanced the car. If you plan to do any autocrossing, I would think that it should definitely have a real and measurable effect.
Have you seen the 2010 FRPP catalog? They have a new aluminum 4 bolt small block crate motor announced on page 77, but there is no power or pricing set yet. On the next page they have the same spec motor in iron; 535 hp and 545 ft-lb for $8800 (a steal!). Once Ford announces the price for the aluminum crate, and the weight of both, you will have a direct comparison.
Peter