If nobody's changed the voltage regulator, one of the easiest ways to tell a W engine car is the bottom hole on the VR had a rubber grommet with a tit on it instead of a screw. Should be no thread marks in the bottom VR hole on the radiator support. Also the wiring is different. The hot wire from the battery to the VR should be a 10 guage on the W and a 12 on the 283 if I recall correctly. I think the starter wiring from the firewall had a connector inline on the W engine and the 283 did not.