I have a couple of N scale passenger cars that I am using for a project that I have installed either 903's or 905's, I don't remember which. But they are working very well with no problems on curves or switches. They are also working well with micro trains regular N scale couplers. They look more to scale than the N couplers and provide a little better close coupling appearance. I have them body mounted and was going to body mount some on my other cars and locos, but I prefer the truck mounted couplers so i'll just use them on the rest of my project cars.
I have replaced all of the couplers on my Bowser cabin cars with 905 couplers, primarily for appearance, and have experienced no problems to date. I haven't tried them yet on any other cars out of a concern for their ability to stay coupled in long trains. I'd be interested to hear about the experience of others using them in long trains.
I am not making a project of changing out all of my cars to Z couplers, but on the ones that I have done, replacing Rapidos or when doing an undecorated car, I use the Z's. I have 9 3/4" radii and have never seen a problem. I would suggest you do one car, and load up a long train behind it and run it all over your layout. You will soon know what the limits, if any, will be.
You'll have to add a mounting pad for the Z coupler. So long as the body of the coupler sticks out slightly from the platform edge, you should make 9 3/4" radius. When you make that mounting pad, make sure there is no interference with truck swing; using a flathead-type screw (Walthers and elsewhere) instead of the provided #@&! M/T ones will help clear truck axles, if that is a problem. It probably won't be a problem for 34' Overtons. The practical limit for a train with all Z couplers is about 50 cars weighted roughly to NMRA specs. I can live with that on a home layout, but for an NTRAK or club layout you'd want to use the regular N couplers. Aside from occasional weak coupler boxes that might just blow up, the engineering plastic gives enough so the knuckles open. The knuckles are still intact/are as good as new afterward, but the material does flex under a heavy enough load.
