If you are old enough - back in the 1980's all major airports had a CMC Speedster or Gazelle in their lobbies. That's what eventually created Speedster desire for me (and fact that first car was a '57 VW). Other than those - most were owner built. The build manuals are here under the Library tab. One diagram shows the massive steel support frame. I'd hesitate to buy from a dealer - find one from an owner.
Cars/Kits were reputable --- it's the company that was finally shut down by Florida's State Attorney General in 1992 for being disreputable!