I'm considering buying a late build date 03 Mach 1. Is there any truth that Ford improved the heads (i.e. grinded exhaust ports) late in the model year to improve performance? Supposedly the better heads have blue markings on them and flow noticeably better (as per a thread on Mach-1org web site). I'd also like to know if the new exhaust systems on 04 models increased horsepower. Anyone out there know the facts or have seen dynos that prove this? I'd appreciate any help as I am looking to buy a new 03 or 04 Mach 1 right now.