I did have a Beck/Merlin 0-6-0 Kit and it had a solid Brass Chassis. I would have thought that by now they would all be doubtful runners unless in the hands of anyone that can give them knowledgeable TLC.
Why not look at a Regner at around £500 Willi or Conrad could have a few Body Mods to be suitable. Or is Steam Trams are your thing Otto at £660 is a great little beast, I have one of these. Or if your Budget is lower, then Max at £275 will be great fun. Put a Steam Tram (Dummy) Body on it and Job Done.
I would say that if you cannot see any 2nd Hand Steamer run, do not buy.
Good luck with your quest in the fun packed Live Steam World. Final though, maybe Mark Horavitz of Garden Rail fame might be able to help you. He is quite approachable, specially if you wish to talk Live Steam.
JonD