i forgot you already have a fresh 727. and as Gene said, you "may" only gain a couple of mpg, so one needs to look at the "pay back costs" to see if this is worth the effort.
however, if one wants to learn, is able to fabricate, and just wants a project, then this swap may be something worthwhile.
the quick explanation, it will bolt up, you need to shorten your driveshaft, the transmission mount needs modified, the shifter linkage may/may not need modified, and using the hydraulic unit allows a couple of ways to activate the OD and the lockup converter.
of course it's a little more involved than that, but all in all, is a relatively easy conversion to do.
you may, or may not need to add a "hump" of some kind behind the dog box to allow the bulky OD unit to sit at the same output shaft height as the original 727.