you have not said anything about the atf quality? is there coolant in that?
you state the trans no longer propels the car
hello

if you truly have coolant mixed into your transmission fluid then if the amount is anything more than a tiny amount you have a dying transmission or it is fully dead.

the coolant will dissolve (i do not know exactly how long it takes) the clutch packs in your transmission so it will disintegrate from within and no longer work as you appear to have discovered.

my next route would be to

1. replace the radiator ... they are cheap for piece of mind
2. replace the transmission from a good one at the junkyard

buy a new radiator unless you can find an essentially new one from a junkyard

transmission failures are no that common so you will find many good ones for a few hundred dollars at the junkyard.

before you buy assess its po's care for it this way.

1. note mileage if available
2. pull the dipstick
if u c chocolate mile run away
if u c bunrt smelling or nasty looking fluid walk away quickly
if u c brownish red fluid if might be just fine
what you want to find is a transmission with low mileage with pink fluid....accept no substitutions...look and you will find it

THIS SHOULD NOT BE A PROBLEM BUT MAKE SURE THE TRANSMISSION COMES WITH ITS MATCHING TORQUE CONVERTER

once you find that special one while it is out of the car and easy to perform

remove the pan and replace the filter screen and clean the pan and install new pan gasket

and then replace the tail shaft bushing and related parts

both of these will be simple jobs while on you garage floor or basement
also as you install it install it onto a fresh transmission mount