66 dart 904 tranny problems

the car had been fine no problems left late to run to store and i lost 3rd gear got to gas stion not even 1/8 of mile away from house got gas made it home in 2nd doing 10miles and hr. leaving gas station realised i had no reverse. kind llost here i un hook kick down cable and it work in rev but it wouldnt engage till 900rpm drove to end of stret and it worked in3rd fine didnt make snse. parked car. i was going to to jack up and remove pan before i could i went out next morning came out it leakatleast a qt of trans fluid out. this is a number matching 66 dart great condition except trans and is for sell. on another note an ideas on how to fix my problem i have a 727and a 360 and i heard 727 wouldnt fit. i just need a problem solver or were to start first