Yes, you have the layout correct. A washer wouldn't work very well, as it will more liley bend when tightened that actually hold proper tension on the manifold, which can/will lead to a leak. You can, however, make a suitable replacement (if you can't find the missing one) using 1/4" bar stock. Use the short one you have as a template to get the shape right and to get the hole location correct. That will be plenty stiff enough to maintain proper sealing tightness.
Another trick to help prevent leaks in the exhaust manifolds is to replace the end studs with either a bolt or a short stud and nut. This provides extra clamping force to the exhaust manifold ends.
