not sure what you're looking for, but in the grand scheme of things it depends on the path the heat flows into the coolant, and the basic design of the engine.
In the case of aluminum blocks, for a traditional V-8, they have iron cylinder liners so you really don't figure heat transfer based on aluminum, at least from the cylinder into the block. I don't remember where the majority of the heat comes from and how it flows out of the engine, there was a good article either somewhere here on this site or out in the internet cloud about it.
In the case of cylinder heads, not sure if the majority of heat from the cylinder enters the coolant here, but they plays a big part in engine performance and the ability of the heads to manage the heat is very important! In most all cases iron block motors with aluminum heads outperform iron heads. Not sure where you're going with this, but, you might want to consider cylinder heads in addition to the block when considering heat transfer.