I'd rather shoehorn in a Mustang engine & exhaust than try to make the SHO sound like that. Or you could try changing mufflers. Or you could combine downpipe upgrade with a nice X-Pipe. Have you looked on YT for the various mods people have done? Plenty of samples from shoman, bpd, etc.
You could also try having MRT build a custom exhaust for you, they work with a lot of Focus ST's, might be up for a SHO project.