You should have all the info you need by the rad support # and trans type. You said it has a 904 trans. The /6 904s have a different starter location so it would be easy to tell if the original engine was a /6. If it's a V8 904, then it had a 318. They didn't put a 904 behind a 340 did they?(340 would have come with a 727) The rad support #s should show the assembly plant, year and sequence #.

Here are the #s on my 73.

B...Hamtramck
3...year
159366...sequence #


So the VIN on the car in question would be JH23G0??????? Just substitute your sequence # and the plant code from the rad support.