I scrapped off the paint all the way between the steering box and the shock mount. I'm not finding any VIN #.

Yeah, yeah, I know. "How could you buy a truck without first checking the VIN #?" You're right, of course (if you think this).

I'm not as upset with the prior owner as I am with myself. I know better than this.

Are there other clues on the frame (although the 122" wheel base is a pretty big clue)?

Whoever Gerry-rigged this thing did a pretty good job. It's not that obvious unless you know what you're looking at (which of course I didn't but I do now).