Hey man!
Your best bet is to find a remanufactured T56. I bought a T56 with "30k miles on it" and it ended up being completely shot. All the gears were pitted and the synchros were totally garbage.
With a shop install my total price came out to around $6k to swap an AOD to a T56
Also FYI you will have the computer doing some funky things afterward, I always get an error code for the input speed sensor shaft. (mine is a 99' so it might be a little bit different)