Even if we suppose that this one, lone engine builder said he doesn't lap valves, every other engine builder, car enthusiast, automotive engineer, engine manufacturer etc. says you do and has the proof you need to (leak down tests and much more advanced/involved tests than that)...

Now, I'm not saying you need to lap valves to have a running, working engine, but we're not talking about merely getting a car to run.

One of my friends is a former F1 Engineer now working for McLaren in Powertrain Development and Calibration and has a Masters in Race Engine Design...would you like me to get his opinion on this or is the opinion of everyone else that's chimed in going to be enough?