My motor is smoking!
Old school.........
If you start up the engine and it smokes, right off, then it your valve seals. The oil leaks past the seals when the engine is off and causes some smoke on start.
If while running it, it smokes, it the rings.
On an older engine, it's not uncommon to "blow out" the bottom end by doing a head job (increased compression). The best way to check this is to do a compression test then try it again after squirting a little oil into each cylinder. If there is a marked increase in the compression then there is excessive blowby indicating you need new rings.
That's my 2 cents but that's old school and has never failed me.
Jim