Re: valve cover problem
This was a common problem with the Cifford valve cover. I'm not sure if your's is the same valve cover marketed and vended by someone else.
Apparently they didn't take the time to install/test/perfect the baffle that prevents oil from getting sucked up into the draft created by the PCV valve. My 4.0 valve cover, IIRC, has a plate that extends the entire length of the valve cover ..with only a very slight opening along one edge (you almost can't see it). Any oil slung off the rockers (or just spaying around in there) strikes the plate and drops back down to the head.
If you just want to determine if this is the source of your oil smoke ...put a water seperator in line (like they use on compressed air) and see if it collects oil. I'm sure that you can adapt some type of small bottle ...but being on the suction side you have to seal it well so that you don't bleed manifold vacuum (think of it as a shop vac canister).