how can you tell

VIN will tell you. 8th digit is engine code.

well i know for a fact that them engines were crap, so if it seems any faster then thats a sign of it, i have a 77 mustang and its built up its far from stock, but yes also see if the number on the vin for the engine code matches the code on the engine, it should be a 302 v8 b/c thats the only v8 they made for the 75-78 mustang

Yes it will, my friend just did ,that exact swap, and he had no es use at all. But the only difference was the suspension, not in the motor. If my memory is correct, 235hp and 275 ft lbs for the 2002 crown vic 4.6 motor, 239hp and 282 ft lbs for the 03 motor. its slightly less powerful than the mustang motor of the same years. The stang had 260 hp @ 5,250 rpm/302 lb-ft @ 4,000 rpm.If i was going to that same swap, I'd find some 351 W DO0E heads from a 69-70 motor, you can pick them up at any junk yard pretty cheap, and wake that motor up. you'll get a million people tell you that the GT40 heads from earlier explorer are better, but they uselessly are talking out of there [you know what] The DO0E heads have a smaller combustion chamber 53- 55, and the swirl effect you get in the chamber, gives you better fuel mixture, and the smaller combustion chamber, will automatically raise your compression ratio at least 1, so if your motor is 9.5:1, it will become 10.5:1....hope this helps

Police Interceptors will have the characters "P71" as the model code in the VIN, or "P7B" for 2010+ models, instead of P70 (Stretched wheelbase), P72 (Commercial Heavy Duty/Taxi and fleet vehicles), P73 (Base), P74 (LX), or P75 (1992 Touring Sedan).....hope this helps