couple kadee

I have been converting my old horn hook to the new Kadee's. I have quite a few older bachmann and tyco cars. How do/ what kind of Kadee will fit in the reciever. I can put one in but it is unstable due the the pin being small.

I am just getting into this hobby and I thought that as I purchase my rolling stock that I would outfit all of it with a good quality coupler. I went to the Kadee site and they have all sorts of them in HO scale. A NO. 5, #58, #148 Whisker, #158 Whisker. I am at a loss as to the...