Can't remember interval specs but they're out there, gut feeling every 50k is enough. #6 issues are due to crossover pipe design creating heat but all other cylinder shims also need more attention than any other Toyota shim over bucket design, in my experience anyway. Whether metallurgy or design issue, don't know.
Oh and for rust -
Ultimate oil undercoating guide (DIY Waxoyl) You can go right over rust and this will last longer and protect better than POR15 or any solid coating, or fluid film 1-2x winter
