Perhaps T-Mar will provide some insite into the serial number. I believe that at least some of the Sequoias from 1983-1986 were made by Miyata and that may be borne out by the similarity in the serial numbers. My own 1984 Sequoia is serial M4C20194. I think yours may be an 83 because of the blue color but it is not the same as the earlier Sequoias like andypop1. There are many construction details like how the chain stays are formed and how the seat stays are attached, and the chrome chain stay and dropouts that are more akin to my 84 (dark slate metallic blue). You can check out the specs for yourself at the Yahoo Miyata-Spec group here:
http://sports.groups.yahoo.com/group...983-1986/1983/

In any case you got a terrific deal. The Sequoia is a great bike.

Jim