[djacobsen  quote]Early  Lionel HO was produced under license by Rivarossi and may have a horn hook type coupler.
 ...snip...
If your acquaintance has rolling stock with the hook & horn type, it would be easy for them to convert over to knuckle couplers. [/quote]

I always had a little bit of "trouble" mounting the usual (KayDee brand in my case) knuckle couplers to Rivarossi equipment as their couplers are/were truck-mounted and I wanted to body mount them. This was HO.