Is the black one, possibly a factory prototype or very early import that Rockford would have shown to dealers?
The ad says it's #00173 and if that's true... it's an early 175. However, read the "documentation" in the ad and then read this.....(see any similarities?)
https://www.bike-urious.com/rare-racer-1966-bridgestone-175-dual-twin/Then on the old Jim Trader site there was a "The Rockford Motors History" that stated this....
"In late 1965 Rockford seen a need for a pure performance machine that could compete in American Dirt Track racing and persuaded the Bridgestone factory to build a 90 & 175 racer.The units were released in 1966 and was an immediate success and even winning the famed Daytona International race in 1966."
So I have no idea what's going on here. Like I said.... I'll let y'all decide!