The heat sink is actually a great idea, production cylinders are always thin to save metal but I wonder what a big chunky cylinder would do?
It might expand unevenly with the ports, this was a major issue designing 4t heads, but we were fighting with much smaller wall section and much higher forces. When we prototyped we would make them out of a big billet with drilled water passages and use the temp measurements to feed into the FEA for the casting design.