i like the bare metal look of my block/heads, but i don't want it to rust, of course. i've seen a few different brands of clear engine enamels and paints. duplicolor, mostly. are they any different from the pigmented types, as far as durability, discoloration, etc.? are they meant to be used as clearcoats only? i'd also be willing to try the enamels that mimic the look of cast iron, if it would look good and be more durable.