If the car has true history "back in the day", the guys at VRG might let you run it.
It will help if you have some old photos or old race documents about the car.
The modern Mustang II front-end will not thrill them, but you may be able to justify it as a "safety update".
If they do let you run, they may consider your car a "special" like the various Devins and Ambros that already run in the club. VRG is a great club. If you click on "My Race Events" at the bottom of this message, you'll see examples of VRG events.
VRG Website:
https://www.vrgonline.org/
You might also try to write to Mark Palmer (at VRG). He's a good guy and can give you good advice about this.
Here is Mark's e-mail address:
mgvrmark@hotmail.com