Torqueflite 6 Automatic Trans not shifting

Hey guys,
I'm having a problem with the automatic trans in my 1964 Dodge Dart. The obvious symptoms are that it refuses to shift into any gear and I can't seem to get an accurate reading on the dipstick. I know I've put in at least enough fluid that low fluid shouldn't be the issue. Other factors: I just replaced the trans filter, as well as adjusted the low and reverse band adjusting screw according to the instructions in the service manual. There was also an incident where the brakes went out completely and the parking lever was thrown on to try and stop the vehicle. There was enough momentum however that the parking lever failed to stop the vehicle and it continued to roll anyway. Not sure what kind of damage this could have caused.
Any thoughts on what to check or try first? What are the most likely scenarios for a failure of this type?

Thanks for any and all help,
-T.
Author: TeaCake