Thanks for all your input. I have checked for vacuum leaks, the car is properly wired, new O2 sensor, etc. That is what is driving me crazy. The only way I can correct the O2 location is to make up some new headers with shorter runners, longer collector, to get the O2 sensor farther away from the 4 pipes, closer to the engine, and farther away from the slip joint of the muffler. I think I'll just hang a carb on it and be done.