Kadee makes couplers to fit all the horrible mounting situations that have cropped up over the years. They have two basic styles -- the box and the contraption.
(Incidently, these are called draft gear boxes.)
The #5 coupling drops straight into Athearn kits and many other manufacturers use the same box. Kadee's plastic box fits these as well. Kadee makes them with different shank lengths and with the shank mounted hign, middle or low. There seem to be metal and non-metal versions. There are also "scale" versions where the head is smaller and shelf versions for tank cars.
The other mounting is the contraption. It's intended more for screwing to floors and has a similar variety.
There are a set for the NEM European standard box.
Look at Kadee's web site. They should have a list of which coupler fits which cars. (The list may not include really old cars.)
They also have a sample pack with some useful tools. I suggest you buy one.
