well it's not a production car ,should of been but John Colletti, one of Ford's best personal and former leader of SVT put a BOSS 429 V8 engine in a 1995 mustang gt. Jack Roushe helped build it as well. It created 855hp. 0-60 1.9 sec. It's actualy a 420 but heres the link. its awsome
http://www.mustangblog.com/blog/1017326_jacks-toys-episode-1-boss-429-mustang