-
If they're Shimano thumbies then SRAM won't work unless you can find one of their ancient Shimano-compatible derailleurs. I would go with a 7/8/9-speed Shimano MTB mech (which will have correct pull ratios), then whatever cassette you like. Sunrace do an 8-speed 11-40 which you can find for £20, I've got one + love it. Might need one of those £1 RoadLink things.
It is cassette is it, not freewheel?
back from a week away and thumbies have arrived!
now I need to work out which parts will work together to give me a usable range of gearing.
I'm thinking a 1x8 setup, with possibly a megarange cassette. not sure if that means I need a long cage rear mech, do I need to stay with Shimano or can I go with sram, will the pull ratios work?? confusing!