The C303 is fitted with a B30A Volvo engine. It is using two Zenith-Stromberg carburetors. The Volvo 164 had the same configuration, and you can get parts from various web stores using 1971-75 Volvo 164 model with carburetors.
I had to replace the Rocker Assembly since it was too noisy. It is hard to find spare parts like this, but I found remanufactured assemblies at Rocker Arm Specialist store. The quality is good and the price is right ($130 for the whole assembly - VO-30)
This is the rocker arm assembly received from the Rocker Arm Specialist.
