Yes, you can do a lot kitbashing locomotives in N. It takes time and ingenuity, as well as magnifying glasses. There are not too many detail parts available, but sometimes you can salvage pieces off junker engines etc.
Being a New Haven fan, my first attempt was a pair of FA locomotives into an electric NH EP-5. I tried several variants on the FL-9, but came closest by bashing two Rapido FP-9 shells to get the length, filling in and moving portholes and roof details. I used EMD 6 wheel truck frames epoxied to the working four wheel frames to get the rear truck, and a very long coupler. I am currently working on partial conversions of Kato/Tomix flatbottoms to give the general impression of NH locomotives.
It is not always possible to get the exact details as in HO, but N is a bit more forgiving because some small parts are not visible. It is possible to get the general features and dimensions close and to custom paint them in your favorite road. If you haven't done much N kitbashing, try a few cabooses or work cars, chopping, cutting, filling, swappinf to get some items for your favorite railroad. Then try an engine. Good Luck. Roger