There was a thread on here a (long?) while ago if you can find it. The first thing to do is find some of the yellow track cleaning coaches at swapmeets - you don't need the track cleaning gubbins - and swap the chassis as the track cleaner has scale height buffers (then flog off the unwanted bits at another swapmeet). The roof can also be lowered by taking off about 1mm at cantrail level (there's a ridge there to guide your craft knife), cut down the ends to a lower profile (I used an old 'Smash' mashed pototo tin for a guide and also to form a new plastic card roof. Add roof detail to taste. That gives the coach a whole new look. Block off some of the windows to make a brake compartment.