Hi Everybody, I am wondering whether I can run unleaded petrol (shell Optimax) in my mild A12, the motor has a GX head on it, with double valve springs etc. Apparently to
run unleaded, the valves need to be steel, with hardened seats?

Could anybody enlighten me as to what valves and seats the GX heads came out with?

Your valves should be ok, they are actually a form of stainless steel and therefore harder than the current chilled and hardened cast iron seats.The wear and recession is caused by the
harder valve pounding its way into the softer valve seat. Fit hardened valve seats and try lapping your original valves into them before splashing out on new valves.Also while it's apart
check for wear in the valve guides and replace the valve seals. I thought Aussie still had the option of high octane petrol which won't stop seat wear it will certainly help stop
pinking. Here in NZ we have to run our cars on weasels piss and getting modified motors to run as well as before is near impossible without adding ( illegally ) avgas. Remember that the
new fuels contain a lot of toluene which loves eating rubber so replacing hoses to fuel injection spec is a good move as well. Hope this helps.