I don't know the 6500, but is it Octalink? You are limited to matching the bottom bracket for sure... or you need to change bottom bracket too.
Of course, if you are changing the crank, the extra cost of a bottom bracket shouldn't be a deal breaker.
You could do a search in this forum to find some recommendations or warnings about specific compact cranks.
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Slow Ride Cyclists of NEPA
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