The converter for the 68 904 in my converter catalog and others says it fits 318" and the 6 bangers. One being slightly higher in stall than the other. But, they will have different stall speeds depending upon the engine. If your old converter is an original factory converter, it will be unpainted and it may have a decal on it.l The triangular one will have LO STALL printed on it and the egg shaped one will have high stall printed on it. You stated earlier that you didn't want a used converter. I mean no malice towards anyone that is trying to sell a used converter, but with them being a welded together unit, how do you know what condition the inside of it is like? Up to 10 years ago, I worked for a transmission parts supplier that had their own converter rebuilding facilities. Virtually every converter that was cut open, required at the bare minimum a 20 bath in the hot tank. There is material that can only be removed via this method.