Welcome to N scale

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This is an old N scale locomotive very similar to a N scale Minitrix model of the same period 

First be sure the loco state is still good and useable; she is at miles away of any running standard of today N scale locomotive so this must be considered somewhere.

I can only encourage you to use Micro Trains couplers the little brother of the well know Kaddee coupler.

First I would check the conversion couplers kit offered by MT one is for sure suitable.

For  the front coupler MT offer coupler which are just a drop in the old Arnold Rapido coupler box, this kind of coupler is offered with some différents length of shank to give more clereances in curves.

Same for the back one, but you can also use a 1015 with a small coupler box fixed in the frame of the locomotive.

It's better to use fixed frame coupler for a better coupling action.

It's also possible to refit original Arnold Rapido coupler in the original coupler box.

Good luck