valve seals??

Do a compression check first, see how different they are. If there's oil in the cylinders it will bump the compression. And if it is smoking due to guides, just replacing seals is only a temporary fix, more than likely will need the head taken off and either new guides installed or guide liners. I've put several motors with no valve seals at all and good guides, and they don't smoke nearly as much as a motor with valve seals and bad guides.

But first do a compression check.