Ok. If you want to use the 727 here's a picture I modified with an arrow pointing to the 2 bracket mounting tabs it has to have for a factory floor shift. A truck trans. can have them but most don't.
BTW: you realize your going to need a new driveshaft with the 727, right? Not positive but I think the shift linkage may be different also. The cooler lines will need modified also.
JMHO but if it were mine I'd rebuild the 904 before I went through all that work just to lose 30 HP and 2 mpg. Again that's just my opinion. You do what pleases you.