I have an old Peugeot and need to replace the cassette, but I'm not sure exactly which one will fit. I've taken the old cassette to several LBS's and they all say nobody makes them anymore. One told me it was a Shimano 600ex. It's a 7-speed cassette with the following gearing: 13-14-15-17-19-21-23

I'm not sure of the year of the bike - I'm guessing somewhere in the 80's. It's got a Reynolds 501 frame, downtube shifters, Campagnolo 700 wheels, Shimano 105 components.

I found a cassette that looks similar at loosescrews.com but it says it's for Shimano UG - and I'm not sure if that's what I have or not. Is UG the same as 600ex? This is all new to me, obviously. The gearing on that one is slightly different but would be an improvement, I think.

Here's the loosescrews.com cassette:
http://www.loosescrews.com/index.cgi...d=931227318491

And here is the bike, freehub and cassette. The tag on the hub in the 3rd photo says "Shimano 105":