Those are great cars. You can probably do some research to check the casting numbers on the engine to see if it was the original engine in the car, given the resulting engine date versus the vin # build date. Try posting in one of the other forums on this site that covers that year model specifically. The guys over there are more knowledgeable than those of us here in the 2005-2006 forum.
2005 Satin Silver GT 5spd, IUP, ICAP, bullits, active alarm, lug locks, side a!rbags, shaker 500, XM Roady 2, JLT cold air, Xcal2 w/ SCT 93 oct tune, & custom fab'd ram air duct, BMR Sway Bars, Hurst Competition plus shifter
Custom blackout on hood and trunk with Steeda street wing and Ford Racing hood pins