This was posted on the SOHC4 site too. The discussion there indicates that the frame may be much rarer than the engine. It will be interesting to see what it goes for.
Mark B1969 CB750 sandcast #97 restored - Sold
Restoration thread link1969 CB750 sandcaxt #576 - Sold
1969 CB750 sandcast #1553 - Sold
1969 CB750 sandcast #1990 - Sold
1969 CB750 sandcast #5383 restored - Sold
Restoration thread link1970 CB750 K0 restored - Sold
2010 H-D Tri Glide Ultra Classic (Huh?)