Example of a reasonable donor frame

Doug Burton

Zen MBB Master
http://richmond.craigslist.org/bik/3831794496.html

Low top tube, can be changed from 24 to 26 inch wheels with a little ingenuity...

Downside is it's probably steel, so the finished bike may be in the 45 lb range.

But this is the goemetry you're looking for.
 
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