When the motor is cranking, if I remove the oil cap there are puffs of smoke coming out, presumably exhaust.

Maybe this is from cylinder 5 and the valve seals are worn? No real experience with the 6, but it seems strange as you have a cold engine, so no oil vapor, are you sure about the timing?

- The new spark plugs are already fouled black after only a couple dozen times of cranking. They're covered in carbon, completely black. Does mean oil might be getting sucked into the intake?

Right, because the system keeps throwing more fuel in there, so engine is flooded (so to speak), need to clean or replace plugs. Had this issue with my VW a couple of winters back.

- The voltage at the connector for the CMP cam position sensor doesn't match what the Chilton manual says, and Chilton says this indicates a problem with the circuit. My other 960 also doesn't match what Chilton says, although it also doesn't match this V90.

You got me on this one.

- The coolant temp sensor in the rear of the head is not connected. It appears it never was, because I don't remember disconnecting it, and I can't find a connector/wire for it anywhere in the engine bay. However, when I disconnect it on my other 960, the motor has trouble starting, which makes me think it's important for that to be connected.

Seem like a great clue to me, if this is the temp sensor for the injection/ecu, how will ecu know what temp engine is at, probably goes to some default value, but I'd probably hook it up and double check cam/crank timing.

Good luck, Mike