MuuMuu101's 68 Dart, A Learning Process...
My money is still on the throwout bearing. Be nice if it is only low fluid, but I highly doubt it.
If it is rattling / growling in neutral......I do not think more fluid is gonna cure it. Might help it, but more than likely gonna need some new parts.
if you get lucky ....do not hesitate, buy some lotto tickets while you are hot.