People like BM and others used to sell converter flex plates that were weighted so you could use a neutral converter behind a 360. Some of them had dual drillings for smaller converters.
ALSO MAKE CERTAIN the 904 is not an early one with the small converter snout, which will not pilot into later engines. I forget, 68? 69? and later. 67 / earlier were for certain small snout
Indeed they did put 904s behind 360s. I believe Cordobas and stuff like that. This is a 1971 transmission, so I think the converter snout is correct for the 360. I think you're right though.... '67 was the last year for the smaller snout.