You only need them if you want the engine to run right. The rings don't seal vacuum, but they do align the manifold with the cylinder head ports so the gasket can do its job. If they aren't there just slice off a short section of exhaust tubing and cut the circumference to fit the counterbore in the head and intake If you want to get fancy with it, make the cut at an angle, but a simple squared-off cut will do it. Just keep trimming until the ring is a snug fit.
Jerry
