Purely on speculation, I would guess that Porsche found that the suspension, in its early configuration, was not robust enough to handle the forces it encountered and that they could increase the car's reliability by adding reinforcements to distribute some of the loads when racing.

The front A-arms on the early car appear to have a very narrow base where they connect to the small-diameter-tube space frame. By putting radius rods (sometimes they're called tension-compression rods)to transfer some of this load rearward into another part of the frame they could spread out the loads over a larger part of the chassis and improve survivability.

Ditto the rear suspension, only the forces go both ways on the rear.... pushing the wheels forward on acceleration and pulling them rearward on braking.

The number 12 car didn't have the radius rods in its first iteration. They were added sometime after the Dutch GP on Gurney's car.