There are coatings on every Mazda motor ever run, it is called chrome plate. The factory processes are not called out in the ITCS any more than every other stock part is specifically called out. It is still legal to use stock parts and processes. Many cams are nitrided from the factory, are they illegal too. Many more are parkerized, illegal?. It has always been legal to build or repair to factory spec and process. No different than the remote res shocks on the S2000, if it came factory it is legal. Alusil is actually a coating in that there is a special honing process to impregnate the surface and then the pistons are tin Plated to not gall up. So under a strict read the 944S2 would not be legal stock because of the coated piston skirt?