I would think the cylinder heads refer to the Stromberg and Weber heads.
Back when I was racing, I knew a guy who raced a TC. He tried to get the SCCA to allow BDA heads if I remember correctly, on the grounds that the BDA head was the next iteration of the Kent engine development and because the Datsun 240Z (and 260Z and 280Z) had a torque and power advantage (not to mention Datsun support) over him that his lighter weight was not able to overcome (Jensen Motors' TC not withstanding). They never allowed it. Now, I don't think that SCCA production classes are controlled by FIA homologation, but I would think that FIA homologation is likely a factor in some decisions.