Grind away the big bulk stuff on the plenum the ridges bumps round the plenum out smooth with a grinder wheel lightly
With a fine wire wheel for a drill you can remove the gray paint and the 2500 from the valve covers.
lightly grind the aluminum pipeing for the turbos then goto a 100-120 grit and some raspy files to fine touch it dremel is your friend to.
when you do all the rough work goto finner grit sand papers then when you get to about 800 -1000 + grit S.P. your about done grab some mothers polish and keep going if you want the bling! if you like where you are at there which is more the brush finish which i like more then the bling look then stop otherwise polish away with mothers and it will look like crome
some good cleaners like commet are like verry fine S.P. and almost polish it there is other compounds that work miracles also like walnut blasting surfaces. the walnut pieces polish the surface without hurting it.