My concern would be that an 8sp RD might be too narrow for a 7 speed chain?
We could raid my RD bucket and do a trial and error session - I think I have a Deore LX in there somewhere, and I'm even willing to let you do all the work.......
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"Love is not the dying moan of a distant violin, it’s the triumphant twang of a bedspring."
S. J. Perelman