I'm far from any kind of expert ,I only know about 10% of what I should know about these cars.
I do strongly suspect that what you have is a Kirban's speedometer overlay, the 85 mph speedo is under it. Hopefully the peel off backing on the overlay won't pull the original silk screened numbers off if you decide to remove it and go back to original.
BTW, that part number is for just the clear plastic lens on the front of the speedo.
From the Kirban Performance website -
1984-1987 Regal -
“145-mph SPEEDOMETER FACE PLATE” DECAL
Our 145 mph speedometer decal is used to convert the reading from 85 to 145 mph on a stock faceplate.
NOTE - This 145 mph speedometer decal is NOT for a digital dash!
It’s an inexpensive solution to the mediocre 85-mph speedometer found in all 1984-1987 Regals.
Until now you only had two choices… buy the entire gauge cluster similar to the GNX or buy another core and pay $175-$225 to get yours refaced and recalibrated.
Our solution is simple. Most major cities have companies that are able to recalibrate your speedometer. This 145-mph decal is done in the same identical two colors as the original plate. It would pass for a GM original. The new decal numbers go from 5-145 mph, but does NOT show kilometers. The imprint is sharp and easy to read. The quality is superb! The decal is exact size and has the opening for the trip odometer and factory openings in your speedometer panel die-cut out of the decal for exact positioning. You MUST have the trip odometer for it to fit. Decal is made of a high-quality hard, thick material that will NOT bubble and has a peel-off backing to affix to your original face plate.
You must have your speedometer recalibrated once this is applied for it to read correctly. It’s all done in the head unit, usually by changing out the hair spring that controls the actual speedo needle. We do not recommend a simple reducer in the speedometer cable because it will not accurately record the miles you travel. If you live in or near a fairly large city, look in the phone book for a speedometer shop. If none are listed, check with your local GM dealer and they should be able to tell you who can do it. Some of the major radio repair shops also recalibrate speedometers, too (average recalibration cost is between $65-$75).
If you can’t find someone to do it, you can send your unit to us by UPS. We will affix the decal and have it recalibrated locally, usually within one business day. After it’s recalibrated, we will send it back to you UPS Second Day Air. This way you can have it back usually within 5 working days.
PRICING: Our 145-mph speedometer face plate thick decal is $25. OR send us your speedometer unit and we’ll have our new 145-mph face plate decal applied, then have it recalibrated and returned to you UPS Second Day Air for just $129.95. This cost also includes UPS Second Day Air shipping back. Allow 5 working days once we receive it.
HINTS FOR REMOVING YOUR UNIT: We’ve checked with our local Buick mechanic and they are allowed 30 minutes to remove and install the speedometer unit. If you have any problems, check with your own Buick mechanic. The unit comes out from the front. The tilt column allows for easy access. The gas gauge and tech/boost unit is all on one face plate which you must remove first before pulling the speedometer out of the housing. The speedometer cable is clipped onto the back of the unit for easy removal.
6508 - 1984-1987 Regal - “145-mph Speedometer Face Plate” Decal
