Was gpx a 6 speed group? Their center to center spacing differed btwn 6 and 7. I think that should be 7 speed, but really I'm only guessing. If so any suntour 7 speed freewheel or cassette- whichever it is- should work... I think. I think the spacing became standardized w/ 7 and 8.
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fun facts:
Psychopaths have trouble understanding abstract concepts.
"Incompetent individuals, compared with their more competent peers, will dramatically overestimate their ability and performance relative to objective criteria."