Tranny question

That's going to depend on whether or not you have any coolers, what size pan is on there, as well as a few other variables. I'd have at least 12 quarts on hand. (This is from personal experience on a 47RE and 48RE... if you really have a 727, i.e. 3spd, no overdrive, then you'll probably use a little less. It never hurts to have a couple extra quarts of ATF on-hand, though)

Best is probably ATF+4 - however, ATF+3 will work fine, and will be cheaper. Do not use any fluid that isn't rated as Mopar 7176 compatible (such as Dexron II, Dexron III, or Mercon).

Always - pour a quart into the converter, and put a thin film of petroleum jelly (Vaseline) around the snout, so you don't damage the front seal when installing it.

Dexron is the fluid originally recommended in the 727, using it won't cause any harm. The plus fluids are intended for use in transmissions that have lockup converters and/or overdrive.

Wouldn't that depend on what year that transmission is and the OP did not say? My 79 used Dextron II and it specified a Dextron type in the manual (both the FSM and the owners).

Yeah... I'm stuck in post-90ish mode.

Either that or I'm just showing my age :-)