Viper dirt track frame

 This is a very rare Yamaha 500 powered dirt tracker, possibly a one-off. 
Viper frames were made by Delton Teuscher in Champaign Illinois. This style frame was generally built for 250s and smaller twostrokes but there is evidence of at least some Honda XR engine versions too. There seem to be two versions, single and double top tubes. Any further info or corrections welcomed.

http://www.flattrack.com/index.php?option=com_kunena&func=view&catid=3&id=117856&Itemid=0