oil does not compress... like water does not compress. ran HV pumps for years and didnt have a problem thinning oil. and i ran the piss out of that 340. took it down at 35k miles and the bearings looked like the day i installed them, and the clearances didnt change. HV pumps were not designed for putting into loose engines lol.
aluminum heads cool better than iron, and they weigh about 50 pounds less. the eddy heads come with the bigger 2.02 valves. so unless your 360 heads are J heads, you get that benefit as well.