I can't really tell you on the fenders, there is not A LOT of difference between the years, but there IS a difference. I know that some have had success in converting '87-'93 fenders to the SVO.
You CAN NOT just go a put an SVO front bumper cover on your '87-'93 stang. You will need the header panel (already mentioned), along with the headlamps, inner markers, outer markers, hood (with scoop bezel) and any misc hardware.
My question is WHY??? By the time you add up what these parts would cost you (either used, repro, or NOS) you could have a decent amount saved towards owning an SVO. It's a buyer's market right now....save your $$$ if you want an SVO.