If I were you, I would take Dave up on his off to sell you one. Eventually you will stumble across another one. For your Eldorado, I think that would be better than trying to use a modified strut.
The main thing that happens when the engine goes into closed loop is the ECM starts looking at the signal it gets from the O2 sensor. All the odd readings you are getting may be because of a O2 sensor failing. If you have any doubts about the O2 sensor being good I would replace it and see if that cures the problem.
Actually there were two Gibson's. One was a car dealer in Appleton, no longer in business, the other is Gibson Iron and Metal the you pick yard I go to...