Dan, I don't think that info is correct, not sure, though.
The Trans you are thinking of, for use with the adapter was a 727, not a 904. That spacer/adapter ring will not work with a 904, the pilot is smaller then the 727.
The pilot on the 727 converter is the same size as the late (68 up) 904.
A 727RG trans will not fit a 67 older slant six, the converter pilot is too large.
A 727 for a small block will only fit a slant six with the adapter plate and crank adapter (67 down) and adding the annular bushing (68 up).
If I am wrong please correct me.
Edit: It was the original poster that mentioned the 904. This trans must be a 727LA. This trans will work behind the 74 small block without the annular crank bushing.