NOS isn't a place it, means new old stock. leftovers from when they actally made them. (unless you are dealing with nitrous, then it is a brand name) I'm not sure exactly when they stopped making asbestos seals, but I'm thinking mid 70's(?) The absolute best way to go if you had the engine apart is the full circle seal, but it doesn't sound like you really have that option. Just keep it in mind when, and if you build another one of these engines.
