Agree. Strip it down to the bare frame and see what you're dealing with. Then you can decide what to do and how far to go with it. That could be anything from just making it rideable again using existing parts, to a full-blown restoration with upgrades. For sure after all these years you will need the bottom bracket, headset, and hubs inspected and serviced.

Are there decals indicating anything about the frame? That will generally dictate how far you go (how much you spend) on a restoration. If that's a full DB chromoly frame and fork, you have something worth keeping and putting money into.