It sounds as though you've tried to be somewhat methodical in diagnosing the problem with how it's running.
You've said that the (mild) camshaft was degreed in when installed which should make a person believe that the cam timing isn't the issue.
You've tried multiple carbs that you said you knew were good. Even if they weren't perfectly tuned I don't think carburetion would then be the problem.
You inspected the camshaft for noticeable wear and didn't see any. Was the cam run previously in another motor? If it is a used camshaft that hadn't shown an indication of problems in another motor I wouldn't think it's improperly ground. If it is a new camshaft there's always a possibility that the cam grinder screwed up. It's not very likely but without measuring each lobe for lift, timing, and duration you can only assume there's no problem with it.
You've checked the spark plug wires for current carrying capacity and firing order along with the distributor cap and rotor for defects. You've checked the ignition timing and verified it's where it should be. My experience with MSD boxes is usually that they work perfectly or don't work at all. It doesn't sound like you've got an electrical problem.
The presence of oil on the backside of the valves combined with the engine running rough may indicate improper sealing of the intake manifold but I'm inclined to think that your engine hasn't had a chance to run long enough to properly break in the new rings and they're not perfectly seated yet. If I'm wrong that would mean that you've probably got an intake leak that's affecting both oil consumption and air/fuel ratios. I don't think that slight valve seal leaks by themselves would lead to the engine running the way it does.
It still seems to me to likely be valve lash but is there any possibility you've gotten really bad fuel?
