This is a design sketch based on the original CEB Press/Rollers sketchup file. This is not done by an engineer so this may not work.
The idea is to make the roller easily extendable, fit a specific length or curve with different types of guiderails. Also this can be assembled by hand via wingnuts. The guiderails can be 2 + x elements long. The curved guiderails are supposed to be hand-bendable into any curve / configuration.
In a curve, the ubars are directly touching each other on the inner side. The ubars need to be wide enough to leave space for the movement of the rollers. Therefore the curved guiderail could live without the horizontal support featured on the straight guiderails.