Great project! With all the configurations the McKeen cars found themselves in, it would keep a modeler busy for quite some time.
They are all eye-catchers, but I can see why they were so unpopular with their engineers:
http://www.sandiegohistory.org...ary/images/page8.jpg
I guess if the McKeens were built a few years later, they would have seen more modern engines, and I guess some were rebuilt with new drives. The slow-turning, heavy marine ones needed a crew to operate them. Even for their time, the McKeen engines were probably ...ahem...lightweight and powerful.
Here's a forum post on Kadee coupler heights:
https://ogrforum.ogaugerr.com/topic/kadee-couplers-3
As for 3-rail, it's hit-and-miss I find. You will see anything from 3/4" to 7/8" from railhead to top of the coupler. I tend not to worry about "height to coupler center line", as most 3-rail knuckles are sloppy enough to have a fair amount of droop depending on the car.
Just my own observations; maybe there are some club operators out there with standard measurements for large layouts.
