Found some of it of Vintage-Trek.com. The Brochure for the 92 520 states that it had 12-28 cogs. The 93 Brochure doesn't have the specs but the 94 referenced below indicates a Shimano HG-60 11-28 7spd same as my 93. While the 520 hasn't changed "much' since 1983, there has been quite a bit of update going on from 6 to 9 speed, brakes have changed, chain stays have lengthened and shortened, from threaded to threadless headsets and butted to tig-welded frames. Regardless I think they have managed to offer a somewhat "timeless" bike that I for one am happy to own.

apparently I can't post URLs yet but if you go to the web site for vintage-trek dot com and look through the brochures you will find it..