Easy, the EEC IV system came out in 84 and was used till 95 in all Mustangs, so you have a EEC system if the engine is stock.
FYI the difference from Duraspark to EEC is that the EEC has no mechanical or vaccum advance provisions, hence the rotor is fixed on the distributor shaft. Also the presence of the imfamous TFI module on the side of the distributor signals a EEC system.
------------------
Frank W 90 5.0 LX Notch MAC 2.5"cat bk FMS alu ds, MSD coil, MAC shifter 2.73 gears
user site
My 90 Notch and 88 2.3 Notch(88 for sale)
74 Chevy Laguna Type S-3 305 now 454 soon
My web site