tranny question

You can only use a 360 converter behind a 360 engine because the 360 is externally balanced. If you use a 360 converter behind a 318 it'll vibrate like there's no tomorrow unless you knock off the weight that's on the front of the converter to balance it for a 360. Another problem you may run into is if the 86 904 is a lockup and the 79 trans isn't. They won't interchange. Splines are different count and the input shaft is machined different.

If your trans is a foot longer than the /6 trans their not the same trans. All 904's are the same length. Heck even the 727 (the big trans) is no where near a foot longer than a 904. I don't have a clue what you have if it's that long. Post pics and maybe I can tell.