That sounds like valve guides drawing oil under the high manifold vacuum, then no more as the vacuum collapses under power.
If the rings were causing oil smoke it should get worse under acceleration due to compression blowby forcing more oil into the cylinders or out of the breather.
You still need the leakdown test to see if the valves are leaking compression, if so it sounds like a head job is in order.
Will get a leak down test done asap and update the results. Thanks Dieselman.....owe you a drink.....