I would do the stem seals regardless. I had a bad smoke issue and I did the valve stems seals first as I was sure it was that (compressions always bewn good so knew no issue there) and still remained.i did the valve stem seals in situ without removing head.i used the rope down bores method turned out the actuall issue was the stock ct9 I had was fooked.had it rebuilt and hybrided and all smoke stopped. g