To answer some of your questions, the body is in good shape and yes, the motor is buried under the cowl overhang. I am wondering what they could have done while changing the cam sensor that would cause antifreeze to get in the motor? The cam sensor is in the distributor, behind the giant intake manifold and you can't even see the distributor. It doesn't look like they removed the intake to replace the cam sensor.
Do you trust the shop that changed the sensor to tell you if they pulled the intake or not?
I could see the intake being the cause of coolant in the oil but it would be a stretch for it to find its way to the exhaust from there. I suppose it MIGHT be able to migrate from the water ports at the front and back of the manifold/cylinder head to the #1, #2 or #7, #8 intake port but that would be a perfect storm kind of scenario to have a gasket breech that much distance without it leaking visibly elsewhere. I don't know if it's possible for the intake to crack or perforate into the plenum from corrosion but that's unicorn territory too I think.
Have you pulled the plugs yet? That much coolant on the floor from the exhaust is going to show on the plugs. If it shows on one of the 4 corners you might have a faint hope of a cheap intake gasket swap fix but in any case it should point you to whatever hole is causing the problem and which head needs to come off.
The bucks down solution at that point I think is a trip to the local pull your own auto recycler on all engines for $199 day.
Kevin
