Complete agreement humble sabot - Incredible imagination, creativity and execution, a lot to admire - body, chassis, wheels and suspension, all made of - wood. I'd describe them as material heretics and design subversives.
Welding 4130? That's quite a skill set. You might like these downloads. Tony Foale is a motorcycle chassis designer.
http://www.tonyfoale.com/software.htm
Some Other Links
http://www.eurospares.com/ Eurospares Motorcycle Chassis
http://www.eurospares.com/graphics.htm Eurospares Chassis Photos
http://www.eurospares.com/frame.htm Eurospares on Chassis Design
http://www.tonyfoale.com/Articles/index.htm Tony Foales Articles