Viper frames were made by Delton Teuscher in Champaign Illinois. This style frame was generally built for 250s and smaller two strokes 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.
And what can say about the one shown below. Discovered at Mid Ohio 2016, it looks like a test frame for rear suspension configurations. (Anyone with any info?)