ALL Aluminum blocks grow period. This affects rods,mains cam bearings, pistons and rods. Most error on the safe side for things like piston to head etc. The also loose heat very very quickly. Building cylinder pressure is another issue because they loose heat so fast. Most would be very surprised the compression ratios run in really good running stuff with an aluminum block. In general you need to ad compression if you are going from a steel to aluminum block.
We run a LOT of compression ratio in my stuff and the Vette. On the reverse side you can run a fair amount of compression in an aluminum block on pump gas. We have done a few in the 12.5 CR area and no issues.
Al, have you come up with any amount of compression increase needed to offset the effects of an aluminum block? I calculate compression by figuring in the block deck increase due to heat. My cold piston to head is .040, and use +.010 added to below deck measurements cold, since that is where it will be under load. But i doubt that will also account for rapid heat loss due to the block being aluminum, which will reduce power output more..
