Damn near everything will swap over, if you get all the parts to swap from one vehicle it will work in the other (although obviously you may need to do alot of work if converting from carb to EFI, auto to manual, etc.). Basically the big differences lie between the cars with the 5.0L/Heavy Duty suspension/drivetrain and all the others. The 5.0L's have quite a few parts that would be required to swap with others (for example, the front spindles and struts for the bigger brakes, along with the master cylinder, maybe brake booster, sway bar brackets and sway bar, etc. etc.) What is the exact swap you're looking for, there are too many variations within the years to really give you a 100% answer. good luck
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'84 Mustang 5.0 LX
My car