Thought I'd share my project. Started life as an XL600R. Main frame/cradle and engine are the only things that will be original. I've put a lot of work into it, still have a lot more to do.... Final tank will be a custom aluminum, that'll be shaped like the old CZ tank, only sitting down on the frame, even with the seat pan.
Bikes that have donated parts:
2006 KX250f forks
2006 CRF250 swingarm
2004 CRF brakes
2012 CRF250 hubs
1982 CR250 shock
1999 CR250 linkage
2002 Ninja 250 dog bones
2003 CR subframe (some of it)
There's probably more; I'll add it if I remember.