Excess engine smoke from 2004 XJ8I own a 2004.

Excess engine smoke from 2004 XJ8I own a 2004 XJ8 and recently we have replaced the engine due to head gasket crack. Now the new engine is causing so much smoke that covers the entire car. I have recently replaced the O2 sensors (cost me $750 for 2) and the car still smokes a lot. After talking to a different mechanic they said this: "there are two possibilities: 1) to start the car and let it warm and open the engine cap; if the smoke comes out of the top then the engine is no good and must return it back to the original seller. 2) If no smoke appeared from the top, that means the oil from the replaced engine has turned to a "Cake" and needs to be flushed out. The way it works is that when the oil is pumped up to the head gasket, it must drop down through the valves into the bottom of the engine housing and that is not happening. If there is an interruption of any kind, the old oil starts burning by mixing with the new oil and create very thick black smoke as it appears in my car. Solution: open the spark plugs and look at the end of the tubes and if we can see the dirt built up then use air hose to flush/push down the dirt/debris into the bottom of the engine, then open the screw at the bottom and flush/push down the mixed oil out of the engine with the air hose to get all the mixed oil (cake) out of the engine. After making sure all the mixed oil is out of the engine, then tighten the screw back at the bottom and pour new synthetic oil and look for smokes. My question is; would this be the ultimate remedy to our problem? Because I have called the mechanic and he said to take a photo of the Heat Tap. I don't even know what taht is. Can some body tell me what the Heat Tap is? Thank you!