The side mouldings are there to protect from bumps and dings. They're level with other doors, so they do protect quite a bit.
86.5-88 had the steel-backed mouldings.
89-92 had the plastic mouldings.
yes, 89+ mouldings will go right in with no modifications IIRC. There is no difference in the sheetmetal, so, there is no difference in the mouldings mounting holes.
You WILL need 89+ taillights to finish the job as 86-88 taillights will not accept the new center piece, so you'll have new mouldings all the way to the rear, but the center will not be the same.
Not a big deal to someone like myself who prefers the 89+ 3-piece taillights.
Not to mention, all you have to do to install the taillights is drill 2 small holes and that's it.
Filling in the mouldings is not recommended if you want to avoid door dings, but if you like the smoothed out look, you need to weld in strips of sheetmetal to fill the void, then finish off with a skim of bondo. If you do it right, you won't even need the bondo.
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