If it's the reverse band, you won't be fixing it with the pan off....its a complete teardown, with box out, I'm afraid.
Depending on year it may be a BW or a Jatco 3N71B - if you can check the model number plate on the RHS of the transmission case....if it says X0410 for the model, it's a Jatco...it should have 3N71B cast on the case on the LHS usually too. I am not sure how to ID a BW, but if it's an Australian built 1970 onwards car, with the BW Automatic badge on the back of the car, under the LH taillight, it's probably a BW.
Best of luck....be careful where you park, so you can roll out easily without reverse....