According to a Ford powertrain engineer I spoke with a couple of weeks ago, The fender mounted solenoid is required on older cars not originally equipped with the PMGR starter, because the ignition switch is not designed for the amp load from the PMGR starter solenoid, and may burn out over a period of time. It will work for awhile but to avoid problems, just use the fender mounter solenoid.
There is also a big difference in solenoids, if you are using a MSD or any ignition that requires a full 12V, the one you need is from a FI injected Mustang, a '92 Mustang solenoid has a diode that will prevent back feeding the electrical system plus it has one small terminal for the start wire from the ignition switch, the other small terminal is deleted.
Buy your solenoids only from your Local Ford parts dept, they are much better quality than just about any aftermarket solenoid.
Dynacorn 67 fastback. Dart 363, Close ratio Magnum 6 speed, 3.70 Eaton Truetrac, SorT suspension. Still in pieces.
'14 SHO with most all the bells and whistles. Stock for now.