There's a reason..Body guys don't like messing around with these bumpers..Especially if they've ever been flexed in any way..
Once the bumper has flexed from an impact the paint on it spider webs in ways you can't even imagine, or sometimes even see..
They won't touch the bumper because of the amount of work that is involved in sanding it completely down..So it can be properly sprayed..
You can't paint over these urethane bumpers that have been flexed, and expect the paint to hold up well..Especially a front bumper..
Your best course of action is to find a used bumper cover from the junkyard for a 89-91 Thunderbird..
89-91 Thunderbird Front Bumper Cover.JPG
The front bumper on the 89-91 Thunderbirds however weren't the best design for engine cooling purposes though..
You have the V6 so this isn't as big of deal for you as it is for the V8 guys..
I consider the 92-93 Thunderbird bumper cover an upgrade over the bumper cover used on the 89-91's..
The 92-93 Thunderbird bumper cover is easily swapped over without any modifications..
92-93 Thunderbird bumper cover:
Just to elaborate a little more on whatever bumper cover you choose to get from the junkyard..It will have damage..That's almost a given..
The best way to prep these bumpers is to have them soda blasted..It's the safest media to strip the paint off with, and leaves a nice surface for new paint..
It's almost like buying a brand new bumper after it's been stripped, and as far as any imperfections go in the bumper cover..
They make a urethane filler that works great on these bumper covers..
1.Buy used bumper cover
2.Find someone to soda blast the used bumper cover
3.Take the bumper cover to a body shop to get painted, and filled
4.Install new bumper cover
Some may argue sanding these bumpers works just as good, but I assure you the time saved and quality of a soda blasted bumper cover is second to none..