Why must a 4.0 head gasket be used for the swap of a 4.0 head onto a 258? Why do I ask? Because we did that conversion on my son's CJ, and it uses a quart of oil every 100 miles. No smoke, no leaks. I am baffled. Especially when it used no oil with the stock head. We did use a 258 head gasket. But, I cannot see why that would cause excessive oil consumption. It runs very well.