I agree with you about disguising them as ex-BR J94s- I've never been a great fan of dressing industrial locos up in fictitious mainline liveries, I'd much rather see them honestly displayed as what they are. My family history is very heavily involved with coal mining, so I'm quite partial to an NCB-liveried Austerity- Even though they're not particularly relevant to my main modelling activity, I still seem to have collected most of the NCB ones Hornby have released...
Anyway, doesn't this look so much better than BR unlined black...
http://farm3.static.flickr.com/2560/3874927102_1359e9a8ac.jpg
http://www.nemodelling.me.uk/NCB%2049-2.JPG