Yep: the sensor is behind the housing (toward the firewall). A new sensor is on my wish-list.

I thank you for these details: there are 4G64 owners who can resource this information now. It's heartening to see these little trucks being restored and cared for again. (The only "bagging" mine ever sees is concrete, gravel or grocery. An occassional garbage bag to take to the dumpster).
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I'm still getting some smoke on cold starts, but it's getting less and less. I'm going to run the engine as-is until the recommended 500-miles head bolt re-torque. That won't be long: I already have 200 miles on the repair.

Next is to address drive-train vibration. The u-joints have issues, and I want to take the drive shaft to be balanced. There is a place in nearby Winchester, Virginia that does this. I will be contacting them Monday, although we're expecting some snow (sighhhhh...again) tonight and this might have to wait.

It was also suggested that the input bearing is worn, so I did order a new one and have it on hand. I'm guessing an output bearing would be a good investment, and will get one soon enough. When the time arrives to replace the clutch, I'll send the transmission out to have bearings replaced. I already changed the gear oil in the transmission and differential...one of the first things I did when I got the truck in September.