Although it's an interesting historical artifact, I'm not sure that a Railscope engine qualifies as collectible. IIRC, I saw a non-working copy go at auction within the past few months for a very low price ($20 or so?).
OTOH, it seems like it would be much simpler to mount a small camera either on a flat car in front of the engine, or attached to the engine itself, perhaps with the shell removed.