400 blocks have siamesed cylinders with only steam holes for cooling. It does not work. Puffing smoke at 30,000 miles. Scrapped every one I got hold of.
I had a 400 in a small motorhome and it had almost no heat for late season races. I was talking to my buddy that ran a local towing service, auto repair and told him I was going to try changing the thermostat. He recommended putting more clothes on and told me their issues. Never gave me one Ounce of problems.