Got my roller bearings.
Have ordered some nice M5 countersunk head S/S screws (hex socket) since these will be visible from the sides of the mirror box.
Now, to really "turbo" my scope, I have ordered the chains and sprockets from these model dirt bikes:-
http://www.youtube.com/watch?v=y_TqX61BLtM
I'm quite convinced that I can make these do what I want.
Time will tell. Wear and tear is not an issue - the chain will probably move forward and backwards a cm or two at the most!
UPDATE:- closer view of chain and rear socket on the model at about 4:25 in this video:-
http://www.youtube.com/watch?v=aOpPy-toeqQ