Hey guys...
When making my build I wanted to add a cover to the rear of my intake manifold to hide a block-off plate for the EGR port. I could have just fabricated a sheet steel cover and painted it but it would still stand out as a cover. I found a way to paint the steel fabricated cover and make it look like the cast aluminum intake.
First make your cover and body work it with radius edges and fillet corners so it looks like it could be a casting. Then prep it for paint and paint it with Rust-oleum Multicolor textured paint. I know, it is the wrong color but hang on. The texture is identical to cast aluminum. When dry, paint over it with metallic paint (or the color you used to paint your manifold or whatever you are trying to match). The result is cast aluminum. See attached pictures.