Nice job! I did the same with my MTH RS3 by shaving the backs of a couple of the Artista conductor figures. Not hard to do at all, but the key thing to do is to tape the cab with painters tape above and below the metal rail so you don’t scratch the paint when removing the shell. Here’s mine -
it definitely adds to the look of the model. Everyone that has an MTH rs3 should definitely give it a try. If I was to do mine again, I’d print out a little cab interior detail from a photo and insert that before placing the figure. I believe @SIRT did this and it looked extremely good.