Were you planning to swap in the 13-50 manual t-case from the BII or stay with the stock 13-54 t-case in the Explorer? If memory serves, the 13-50 uses a different output to the front shaft, so you may need to do something there. Rear output is the same, for either t-case, I believe.
Did you verify the transmission model? I'm pretty sure the FM 146, M5OD, and A4LD are all the same length. The FM145 and TK transmission were shorter, I think. If you are swapping in the FM 146 and using the original 13-54 t-case, you should be able to use your original driveshafts. If you have a different transmission, or if you are using the 13-50 transfer case, you may need to modify one or both driveshafts.