The more you advance the timing the more it affects your fuel mixture, 38 degrees is at least 3 degrees more than i've ever been able to run in a 383. Check your dizzy and make sure the advance is working correctly. You corrected the lean condition, hope you re-jetted it. Wheres your LM1 or 02 sensor? I'd run those plugs, they look fine to me. If it was too lean the electrode would show heat damage, none is aparant from the pic.