Personally I would not get one from a junkyard ford because you don't know how filled with crap it is...Just buy a new one they aren't that expensive.
For what it's worth, I bought my pathy with 210,000kms and now has 380,000 (around 230k miles). Tranny had intermittent reverse issues, but resolved that with a few good flushes. I got lucky. I added a cooler and filter. I've beat the crap out of my transmission (towing heavy loads) and it is still working fine. Though the shifts aren't as nice as they used to be I just attribute it to age.