I haven't changed the oil since the Seafoam, but it'* still very clean. The directions on the can say change it once it'* dirty. I followed directions pretty closely - I put about 1/3-1/2 in the vaccuum lines, 1/3-/12 in the crankcase, and then the rest of that can and another can in the fuel tank (1 oz/gallon is directed - 18 gallon tank).

I probably won't get to it until after the holidays at this point, just looking for suggestions so I can hit the ground running.

Sea Foam in the top end can cause crappage (technical term) to coat your O2 sensors, and even to possibly clog the cat. Pull the upstream O2 sensor and do a visual inspection.

I've done quite a bit on this car, but nothing with oxygen sensors. Where are they located and what is required to get to them?

On the exhaust pipe, upstream from the cat. From up top, look behind the engine in the area just below the rear center spark plug.