Hey, I resemble that remark!
I bought a brand new exhaust manifold for my 1979 head to replace a cracked one. I then decided to do the 4.0 swap and bought another brand new manifold for the new head.
I ended up selling the 1979 manifold for half of what I paid for it last fall.
I still insist that the head made most if not all of the difference on my engine. I count the new, redesigned exhaust manifold as part of the head swap because switching manifolds is required when going to the new head.
The only thing I changed at all that could make any difference is the carb, and I've already explained why I don't believe it's possible that it could have made this huge increase.
The head on the other hand has all the improvements I listed earlier. Smaller chambers for much higher compression. Bigger intake and exhaust valves. Bigger better shaped ports. And a much better flowing exhaust manifold. There is absolutely no way that you wouldn't see big gains in HP from all of those improvements.
Swapping carbs wouldn't hold a candle to the HP the head would make.
Ask any performance engine builder and see what they think would make the most HP gain when you list all of this.