I have an old Roy Thame frame that I purchased in London. (I think it is actually an old Ciocc frame). I built it in 1981 with a 5 cog freewheel. Recently, I found a new, larger gear range 6 cog freewheel at a bike shop and put it on. I was pleasantly surprised to find that it worked, except that the old Campy Nuovo Record derailleur is obviously going to have to be replaced. But with what? I am considering a Shimano Deore which by its description says is for a 7 speed. Will this work, or will the derailleur be unable to limit putting the chain into the spokes? What do you recommend?
Enjoyed your site,
Yes, you should be able to install any of Shimano's mountain-bike derailleurs and get your bike to shift just fine, so you could get any one you like. Just be sure to fine-tune the limit screws so that the range of travel is spot-on and you won't have any trouble with it shifting into the spokes.
The difference from one derailleur to the next is mostly a few less grams, a nicer finish and usually aluminum versus steel in certain parts. So, there's no need to spend any more than you want. If you just want the bike to shift again you can go with the least expensive mountain-bike derailleur you can find. If you wants higher quality and lighter weight you can spend more. The shifting will probably be so similar you'll never feel the difference.
Have fun fixing up your bike!