Athearn N scale FP 45 changing from Mchenry couplers to Micro-Trains 1015 and 1016 couplers:
I used a Micro-Trains 1015 in the rear and a1016 in the front. If you wish a closer coupling you could use a 1015 in both locations, but may need to trim the coupler trip pin of the locomotive coupling to it as it will hit the snow plow on the unit with the short coupler.
I checked the couplers with a Micro-Trains NMRA N scale height gauge and the couplers aligned.
The model may be turned upside down in the case the engine came in as there is a depression that clears the air horn in the lower plastic cradle.
Remove the Mchenry couplers by removing the screw. Save the screw it will be used to install the Micro-Trains coupler later.
With the Mchenry coupler removed turn the model upright and file a very small amount of plastic from the lower surface of the shell coupler opening, only enough to clear the Micro-Trains coupler.