Tom,
Its a mixed bag....
The bad side is that since you didn't take it apart, it might be more difficult to reassemble.
The good side is that you see exactly what you have---no shiny paint over obvious old rust or bondo. If you have the space, and a large enough air compressor, I'd recommend using a small pressure sand blaster to remove the rust and paint---I call it "unpainting". You need to keep the pressure down, and blast at about a 45 degree angle, but the metal is thick enough that you are unlikely to distort it. Here, in Baltimore, the humidity is often so high that clean metal begins to turn brown within minutes of getting clean. And CLEAN is what sandblasting will give you. Sandblast, hit it with some pickle-ex or other treatment to preserve it until you can get primer on it.
It will be one very kool-looking truck.
Are you going original on the engine or going modern?

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1982 300SD " Wotan" ..On the road as of Jan 8, 2007 with Historic Tags