Yes, the clutch will work fine, but you have to switch out the flywheel. The stock 84 flywheel is 10 inches... So obviously you need a 86-93 10.5 inch flywheel to use the 10.5 clutch. Also, yes... an 88 T-5 will bolt up to your 84 5.0 perfectly, no mods as long as it is a T-5 already.
Not sure if the 84 came with the S-rod trany, but i think it did. In that case you need a different bellhousing to mount the t-5. The S-rod bellhousing works for the S-rod trany and the Tremic. If that is the case, I am sure you can find someone willing to swap bellhousings with you on the classified section.