This is only a guess, but I imagine a cast block would be lighter & offer better cooling properties than machined. Also cast you could get the exact composition of alloys. A machined block would look awsome I must admit.

Good luck with the new project, I followed the Should I make this thread from the begining & you silenced the critics on that one, so why should this be different. I would like to give one of your bodies a go but they arent legal in the class I run in.