I'm no expert on automatics but I think it's usually a good idea to
either put in a rebuilt converter or at least flush out the old one.

The idea is that as the old transmission failed debris would be pumped
into the converter.  Then when you put in a new transmission when the
fluid starts getting pumped around the debris will get picked up out of
the converter and pumped through the transmission, damaging it.

Of corse what do I know, in 30 years of driving I've had exactly ONE car
with an automatic, my first, a 60 Hawk. <G>

Jeff DeWitt