the SS headers will move more heat out of the tubes then a steel coated header .i would not powder coat the block or the heads if any of that powder coating gets some were you do not want it .you will have a hell of a time geting it off . and it may not stick so hot on some of the machined spots on the block. and heads this may be a good spot for it to fall off? it will hold heat in? why paint or powder coat a aluminum block??