Before I go to the junkyard, are there any differences between the 5spd pedal assemblies in the 4 banger and V8 cars? I don't see why there would be but I thought I would ask first.
The GT gas pedal is wider on the '87-'93 model years. I have the narrow 4-cyl one. The wider pedal makes for WAY easier powerbraking with a manual tranny, as you can sidestep the brake and gas with one foot and work the clutch with the other. With my narrow pedal it's practically impossible. The Turbocoupes also have the wider pedal.
A 4-banger pedal assembly frame will work. However, the clutch pedal arm is shorter on a 4-banger Mustang. You can use a 4-banger pedal frame with a 5.0L clutch arm.