Nice truck! I had a 1985, same body, 5 speed manual transmission, 2.8 V6, single tank, forward of the rear axle.
I can see the hood release in your interior pictures. The tilt lever (if you have tilt steering) is on the steering column, left side (but you've already found it, if it's there). The tank switch (I've seen it in pictures) is up on the trim strip that runs across below the cluster and the cubbyhole. It's also not the parking brake release, or the hood release. By process of elimination, I can't seem to account for a mystery lever (pedal?) that appears to extend from the bottom of the dash, in the center. I can see it there, forward of the gear shift. Have you figured out what it is, yet?