Are PCV needed?

Yes you need to run a PCV. The breather is desinged to allow air into the crankcase to equalize the pressure drawn by a PCV system via engine vacuum. It cannot sufficiently purge all the crankcase gasses, even in a newly rebuilt engine, therefore it needs to have the gases drawn out by the PCV. The crankcase pressure builds up in the motor & forces it's way out around the valve cover gaskets & possibly the crank seals. It dosen't really matter what valve covers or gasket you're using. Also, as previously mentioned PCV helps with ring seal. Racers actually try to gain negative crankcase pressures by adding vacuum pumps or scavenging systems to their engines for this purpose. I hope this helps.