The bottom end of a 2004 Mach 1 4v isn't anything special. It won't really handle anymore power than a 2v. However, since its a 4v, it'll respond a lot better to mods. If he is really serious about this, take the car to check the compression and maybe a leak down test. As long as the cylindets hold equal and decent pressure, it should be okay. Then I'd recommend if he's got the cash to throw a blower on it as is with a really good tune, since its his DD, and build a short block to handle some more power.
2000 Mustang GT-Former giggle gas addict
1990 Mustang GT w/ Vortech V3
***resident gun idiot***