Dave can you measure across the flats of the nut? I am not sure if it is turned over or not but am curious as to whether the other side has a shoulder diameter for staking. I am looking at a complete output shaft and it does have a nut, C washer, and a flat washer on the end of the shaft which is right above where they are laying in the pan.
Here is a picture and view of the nut and two washers on the out put shaft.
below is a cut away view with a arrow pointed to where it is if you could look up inside your to see if you can see the shaft and if so see if the shaft still has the nut on it?
If you can not tell if you can see it or not I can go install a output shaft in a engine block and put it back together to see if you can. But I must admit it will be quicker if you go have a look see even if you have to raise her up in the air a wee bit more so you can get your head under her if she is not up higher already.