Is there a risk of warping aluminum cylinder heads if they are bolted to a cast iron block? I was thinking that the two different materials have heating and cooling differentials that might be condusive to warping.
In a word, No. Unless the heads are subjected to overheating, they don't have any tendencies to warp. The heads are clamped to the block and they do expand at a different rate than the block does, but because of the clamping force from the bolts/studs, no warp. If you're thinking of putting aluminum heads on your engine, Go for it.