Vintage-trek.com can help you figure out year based on serial number. The most desirable of the 400 series had Campy components, but I've also seen them with Suntour Cyclone M II, which is IMO a vastly undervalued group - really good performance! All the older steel Treks (prior to maybe 1986) were built with good to very good tubing - msotly Reynolds 531 or 501, but occasionally Ishiwata 022 or some variety of Tange (often Tange 900), and very occasionally Columbus. I've ridden a handful of 400-series bikes from 83 to 86, and I've liked them all
What's special about them is that prior to about mid-1985, they were all handbuilt, and they've generally got comfy, nimble geometries - you'd pay a lot more for such attributes in a modern bike!