Just ordered FORD Racing Shorty headers

Someone wrote in this that they installed JBA shorties and had to change the engine mounts to the more solid ones that Steeda offers. The reason he said was the engine was not exactly centered with the OEM fluid mounts and was causing the header to contact the steering shaft. After installing the Steeda pieces everything fit. You may or may not have that problem when you install your Ford headers.

how much hp increase are we talking about pipe size? Whats the difference between long and sort headers(other then size?) and I'm in california.. will it mess up smog test?