oil rings work either way and if the compression rings were upside down, you would be getting massive amounts of blow-by. matter of fact, it would probably blow the dipstick out every time you revved it up.
it could be valve seals
it could be cylinder glazed
if it has been doing it since you got it back from the builder, it could be the oil rings are not aligned opposite from each other.
how bad does it smoke?
are you sure it ain't leaking?
what weight oil are ya using?
was it bored out?
if not what were the micrometer readings before the rebuild?

seems i always have more questions than answers
lol , Dallas