stanC- those "shafts" are known as NEM Boxes, I'm not sure of the number but you can get Kadee knuckle couplers that clip into them too.
Like wise you can buy European couplers that can fit into Kadee boxes- Mehano in Izola, Slovenia is an example (IHC buy their stuff from them so try IHC [International Hobby Corp]).
What I would do, if you wanted to mix the wagons with different type couplers, is to make one or a few "adapter wagons", i.e.: One side has the knuckle and the other side the European type.
Upside of this: Cheaper than doing the whole fleet of wagons/coaches.
Downside: You need to always run whatever adapter wagon you made in the consist if you are going to be shunting.