I'm not an engine builder but I do have an engineering education and experience. I have never heard of a Ceramic material or coating that helps with heat dissipation. Ceramics can be produced in a wide range of thermal conductivity but are fundamentally insulators (amorphous structure, so generally poor at electrical and thermal conductivity). Most ceramic coatings are used as thermal barriers to protect the underlying material (generally metal) from high temps (i.e. Keep the underlying metal from absorbing heat from the surrounding environment) or to provide corrosion resistance. They are typically applied using plasma spray or electron beam vapor deposition processes. There are some ceramics that have relatively high (for ceramic) thermal conductivity but these coatings do not improve heat dissipation from the underlying metal, they simply hinder it less than other coatings would. They are used where a ceramic coating is needed for other reasons (abrasion or corrosion resistance) and there is need to minimize the negative impact to heat dissipation.
Also, there is not a lot of heat conducted up from the heads and cylinders to the rocker arms. The connection points between the heads and rockers are pretty minimal in surface area (and therefore serve as resistors to thermal conductivity) and the surface area to mass ratio of the rocker assembly is pretty high so any heat that gets conducted to the rockers tends to be radiated away or convectively transferred to the
oil pretty quickly. So I don't see how coating the rockers would help dissipate heat from the heads and cylinders but maybe I am missing something!
Ceramics can be used for abrasion or wear resistance and I could see how this might be helpful at the pushrod cups but I have never seen that done before.
Anyway - still look forward to seeing that beast when you get 'er running!