Al, you certainly have a lot more experience than I do in this area but I can see how a very well engineered aluminum block with thick strong sleeves could provide a better ring seal that a iron block that might be more flexible. Of course ring seal equals power.

If this is the block I am thinking of it has more strengthening ribs in the valley that I have ever seen in a block.

That being said there could be lots of other factors with a completely different engine that could have accounted for the horsepower.

Bill