Instructions for installing Kadee #7 couplers were offered in the March, 1978 issue of RMC. For those of you who may have mislaid your copy,

here's the gist of the short article: Remove part of the "ears" on the coupler itself, using a file. Don't remove the entire "ear"; just the tip of the smaller one, and just enough on the larger one to make it the same size as the modified smaller one. The article suggests that the sides of the Kadee box be thinned, using a file (which will remove the large "nub" on the exterior face of one side) and that the rear of the box be trimmed so that it doesn't protrude past the rear of the installed coupler. Also, the opening in the pilot needa to be enlarged, using a file.
or
I don't recall doing all of these modifications (although I sometimes can't even recall my own name

) since I assembled the couplers
on the locomotive. First, enlarge the opening in the pilot, using a file, so that the front end (the end where the coupler is supposed to stick out from) of the temporarily assembled coupler box will fit snugly in the opening. Next, place the coupler over the pin in the Kadee box, then trim off any part of the rear of the box that extends past the rear of the coupler shank. Trim the lid to match. The Kadee draft gear box is inserted through the opening from the rear, then the coupler from the front, then the centering spring is installed, and the lid is also installed from the rear of the pilot. You can use either the Atlas pin to hold the coupler in place, or tap the hole and use a screw. The latter is the better choice.
I hope this hasn't made the whole procedure seem more complicated than it actually is.
Wayne