Depends on where the oil smoke is coming from and for what duration..
If it is from the exhaust and only a few puffs on start up, i would suggest getting new valve seals installed. (You can do this yourself with the right tools, but if you are unsure of your abilities or lack tools, it isn't too expensive to have done at a shop)
If from the exhaust and constantly while running, then I would suspect the rings or an over pressurizing of the block.
The over pressuring of the block can be something as simple as a pcv valve that has become completely clogged or stuck, where it isnt allowing the intake vacuum to remove the natural pressure due to slight ring blowby.
The first thing I would do, it sounds as if you have already done, which is search for obvious leaks, then determine what you can about the exhaust smoke- just at start up or constant?
Check the pcv valve by removing it and shaking it, listening for free movement by the slug inside, or just replace it since they are rather cheap
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Reading the plugs can lead to some clues about what is going on inside the combustion chamber as well. If a plug or plugs is/are wet with oil, I would deffinately say the rings are worn and if it has heavy dry carbon build up or patchy thick deposits, I would be inclined towards valve seals and or pcv valve.
If it is suspected to be valve seals, then it is a simple fix by merely replacing the valve seals. (I won't get grimey with details on that
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If it is determined to most likely be the rings, there are a few ways to go about correcting the issue.
One way is to have a ring job done, where the pistons are pulled, cylinders ridged and honed and new rings installed and everything installed back into its original location (pistons)
Another way is to yank and simply rebuild (I recommend this way as if the rings are worn, then the bearing surfaces and other parts are probably worn out or very close to being worn out anyway). During a ring job, it may be found out that you will need to rebuild as well as bore and install oversize pistons or replace all the bearings anyway..so....
Another thing to consider is whether or not the engine has been rebuilt in the past and if it was actually done properly with the correct parts...
Trust me.. one set of wrong parts can wreak havok on your engine and your mind trying to figure it out.
My bronco is a prime example of that.
It has a 351w, built stout, all aftermarket internals, big cam etc and one set of overlooked parts which were causing over pressurization of the block to the point of killing the engine much like a clogged cat and blowing oil (yes, wet oil) out the tail pipes. (had the bronco about 3 weeks before discovering what was causing the problem...)
The overlooked parts, were the rocker arms.
The originals were used on top of the big cam when long slots should have been used.
The result was nearly disasterous as the person that rebuilt it, managed to run it for about 17,000 miles while the cam, lifters and pushrods were literally beating the rocker studs (press in) out of the heads.
ALL of the studs were pushed out to some degree with the studs on the #3 cylinder being the worst, with the exhaust valve not being moved at all and the intake valve barely opening enough to let some air in on the intake stroke.
The result of the valves improper opening was that all the compressed gasses in that cylinder were being forced past the rings and presurizing the block enough to push gobs of oil past all the remaining live cylinders, eventually slinging it out the exhaust.
It is fixed now (time consuming pain in my tailbone...) and may be another post in it's own
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