one time, i had a 727 in a chrysler that had no reverse because when the previous owner adjusted the bands, somehow the band strut fell out, loosing reverse. put the strut back in, and all was well for thousands of miles afterwards.
having the 3.9 engine, however, suggests there may be a 904 variant behind it, and i remember lots of stories about the band anchor spot welds breaking from the band, causing the "no reverse" symptom.
in this case, the transmission definitely needs to come out.

unless you always park so you don't need to back up..........