I am new to this forum and it appears that I responded directly to you instead of the forum. I went to my smog mechanic yesterday and checked the state manual that all the smog mechanics use when smogging a car in CA. For the 1986 420 SEL it clearly showed 12 degrees. Starting with 1987 or 1988 it showed that the timing was non-adjustable as you described. Therefore, it appears that for the early 420 SELs the timing was adjustable. Although the car runs very clean, if I had a smog test done it would have failed becasue the timing exceeds the maximum allowable 2 to 3 degrees above or below the specs. Anyone has any suggestions?