I could use a 1974 slant six manifold heat control valve expert!

I can tell you how mine worked before I changed to the 225 and blocked it off. When the engine was cold, the valve would open on hard fast acceleration. When hot, the valve was barely closed at idle, but opened easily when the throttle was cracked. Whether that's "correct" or not, I don't know. On my present manifold, I have the valve removed and the hot air to the intake completely blocked off.