If speedometer working--probably needs new head or repair If speedometer not working could be a bad cable
When it comes to calibrating your speedometer, most auto repair shops can handle just about any car. With that being said, I would try to contact an auto repair shop in your area and ask them about receiving a speedometer calibration.
Need to figure out what's wrong with them, first.
According to my Chilton's Auto Repair Manual : A 1991 Ford Mustang has a ( 15.4 U.S. gallon gas tank )
There are several things you can do to repair your speedometer. You can replace the speedometer cable. You can replace the speed sensor in the transmission.
The best way is to buy a book on your model and see if you can do it. Then! Ask again on this sight for help when you feel confident that you know what your doing to repair the speedometer.
There is no particular class in order to repair a ford mustang. If the mechanic have the experience then they are able to repair the vintage Ford Mustang.
The speedometer itself will work but you will need to take the instrument cluster apart and transplant the speedometer unit from the 92 cluster into the 87 cluster. The speedo mechanism is the same but the clusters are different.
A Mustang Cobra;s Speedometer tops out at 160 MPH. But have been known to exceed that.
I'd suggest you take the car to a speedometer repair specialist. They can remove, repair and calibrate the spedometer.
Loose or failing speedometer cable Speedometer head needs repair