I have 3 MMI 0n30 locos and a bunch of 0n30 gauged SJC / AMS freight and pax cars. I like the look of the 0n3 couplers and will keep them that way. I own a few B'mann pax & freight cars and have converted their couplers to 0n3 height - easy to do except for the hoppers which involved some grinding and filing.
I recently bought a B'mann 4-6-0 and need to convert the tender coupler - looks like it is going to be a time consuming grinding / filing project. In the meantime I did not like the look of the low coal bunker behind the very tall cab or the length of the coal bunker:
I decided to fabricate a taller, shorter coal bunker and think it looks much better. Here is a test fitting photo of the result: