Reasons for excessive exhaust smoke?

If you don't have a compression gage, try turning the engine over by hand. You can do that in a slant by pulling and pushing on the fan belt at the alternator, if no shroud. It turns cw looking at the crankshaft from the front. If you can fell each cylinder strongly resist you (3 per revolution, chalk the crank damper), and you must wait >3 sec for each one to hiss down, then you have excellent compression. If true, it is likely getting oil past the valve stems. As mentioned, the rubber umbrella seals may have rotted.

Don't fear removing the valve cover, as that is a regular thing on a slant to adjust valve clearance. You can change the seals w/ engine in car, but must remove the valve springs and one at a time so you don't drop a valve out of the head (have piston at TDC). But, don't tackle that without reading up a lot and thinking it thru. Ditto for adjusting valves, though less risky.