Shoulder roll bars were mandatory in 1954-55 by the SCTA. A head hoop came in 56 I believe and bracing after that.
Here's a Roadster in 1955 -- looks like no rollbar required. I doubt that RPU was a competitor -- they're a whole lot of hot rods there every year -- more than the number of competitors.
That roadster had a legal shoulder bar. Many were under the body lip. Jack Underwood and his father were there during that time helping other Compton guys and running their roadster and were talked of that era often.
Here is how it looks now as found it was turned into a show car in in the late fifties and shown at the 1960 Oakland Roadster Show by Joe Schwede.
I live out in the middle of nowhere but there's a guy local to me who built a RPU in the 60's and he still drives it regularly. Pretty cool build. He told me how he reverced the eye wrap on his front spring by sticking the ends in his parents coal furnace. Straighten and re twist. He's never had an issue after thousands and thousands of miles. Crazy stuff! More photos of that RPU on Instagram if you do that kind of thing. https://www.instagram.com/p/Ci8yQSUP48f/?img_index=1
The Jalopy Journal
