GN1's
If you do a search, you'll find that some have had problems w/valve guides on GN1's. Are your heads new? Tom says the problem is fixed on the latest heads using a new style valve guide. Hope that's right. I just bought a new set. So many other reasons your GN can smoke tho. Seems to be really intensified when you add more breathing. Do a search on smoke, oil smoke, etc, and you'll see many with the same problem, and some advice on various fixes. Do you have steel shim headgaskets? I ask because squeeze out of the silicone sealer plugged my oil returns, and the valve covers were filling with oil. Perhaps others will chime in here...
Good luck