Do take the cassette off; I bet that you will find a spacer behind the cassette; remove it, and you'll be able to fit an 8 speed cassette that will match the shifter. 8 speed cassettes can be had new in the USA from Amazon for $15-.
Thanks for the info Nigel, I was hopping you'd chime in. I am aware of magnetic SS alloys but in my experience have not come across it in typical use. I read that its used in industrial applications and electrical, making junction boxes and such out of it...........can you think of other uses?
My SS spokes are none magnetic. AS you say some high end spokes for custom wheel builders can be magnetized by hardening process. I doubt there are many commercial wheels like that out there.
I once took a magnet to my LBS, when I was looking to buy a bike, and could nor find any magnetic SS spokes.
Also if its a vintage bike and the spokes are not rusty that's a good indication they are SS..........some very light surface rust at most.
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