3D printing is great, but nobody is doing iron and few are doing aluminum due to the power demand. At the rocket engine company I work for, we have some of the largest printers in the world, but they're printing platens are still only ~15"x15" square. Keep in mind that post printing, you still have to send each part through a Hot Iso-static Pressure (HIP) process and additional heat treatment processes. Its great, but like all things, the more you know, the less great it then becomes. The process still has a long way to go before building larger parts such as an intake, and even further for a block.
Joe