Since it's an older bike, you could prolly just unscrew the cassette leaving you with space to thread on a track cog. Apply some blue Loctite to the threads of the hub, cog and lockring, screw on the cog and then screw on the BB lockring and snug it up tight to the track cog. You may need to redish the wheel slightly. Make sure the chainline is as near to straight as you can get it. Done. We'll worry about the rest later (removing braze-ons etc).