A split-port swap is the 99-04 V6. The 94-98 V6 used a single-port intake with badly flowing heads, Ford upped the power in 99 by using a much better set of heads and a split-port style intake for better power through-out the rev range, this is what gave the 99-04 the additional 40hp. Go to
www.supersixmotorsports.com and they have the kit for ~800~ or you could just swap the engines. If you were to swap the engines you would either have to swap the fuel system or customize your fuel rail to make it work. The split-ports gain power better than the single-ports do.