I recently got myself a 69 El Camino with a 454 in it (not original), and noticed that it was running pretty rich. I took the temp of each header tube real quick looking for one that was not hot to see if I had a misfire, but instead I found that 3 of the 4 pipes on the drivers side were off the scale of my IR thermometer (about 1200 degrees or so) at idle with the engine warmed up. The other pipe on the drivers side and all 4 on the passenger side pipes were around 400 degrees, and the passenger side exhaust definitely smells more rich than the driver side. I took out all the plugs and the 3 'hot' ones were definitely running lean since they were light brown, and the rest were black and wet. I'm already going to get new plug wires for the car since they all look pretty worn and one of them has a burned up end on it, but why else would only 3 of the cylinders be running lean? Maybe the camshaft has some rounded lobes on it and the valves aren't letting in enough fuel?