The only reason I care about the operation issue is these cars will probably be sold
off and I wanted them to be useful to the new owners.
That's easy then: Stick with the MT couplers. It's the de facto standard and no one will want to buy anything else, even if it is more accurate and closer to scale (least of all some sort of odd duck or force-fit conversion). Your weathering will be so good that no one will look at the couplers anyway
for ultimate realism, add track details from Proto87's N-scale selections (e.g., individual tie plates).
Personally I would suggest the ME code 40 flextrack. I've tried the P87 parts, and while I really like the HO spikes for N scale track, I find that the individual Code 40 N-scale tieplates are
so small that they really are quite hard to work with (hard to pick up, and they never seem to want to stay where I put them... whatever you do, don't sneeze near them!). Plus it is really hard to see them, even in close-up and in photos - they just sort of blend in and disappear, unless you paint them a contrasting color.
Ed
(PS Bob, thanks for your
way too-generous comments, BTW where did you want me to leave the suitcase of unmarked $$ this month?)