Ford has revealed a 1966 Mustang Fastback for SEMA with a useful question behind the spectacle: which modern Ford Racing parts actually make sense in an old car? The R125 is a one-off demonstration, not a new Mustang you can order. That distinction matters more than the dramatic paint or the inevitable crowd around it.

Under the hood is a 347-cubic-inch V8 built around a Ford Racing Boss block and aluminum heads, with Edelbrock Pro-Flo electronic fuel injection. Ford quotes 360 horsepower and 400 pound-feet of torque. A Tremec TKX-600 five-speed replaces the period gearbox. Those are substantial changes, but they keep the familiar appeal of a small-block Mustang: a straightforward engine, a clutch pedal, and room for the driver to do some work.

Photo: Ford Racing. Editorial use.

Why the TKX matters in an old Mustang

The transmission choice is more than a convenient fifth gear. Tremec describes the TKX as an aftermarket gearbox with a slim case for better tunnel clearance, three shifter-position choices, and a 600-pound-foot torque rating. Its multi-cone synchronizers are meant to make shifts smoother at higher engine speeds. In a 1960s Mustang, where the floor tunnel and shifter location can complicate a swap, that packaging is the real engineering story. It does not make every installation bolt-in; mounts, driveshaft, clutch setup, and clearances still need checking.

Ford also uses the car to show new two-piece valve covers with interchangeable top designs, captured O-ring seals, and integrated spark-plug-wire routing. Those details sound small until you have chased a seep around an old cover or tried to tidy wires in a crowded engine bay. The design allows a cosmetic change without replacing the complete cover, though actual fitment and pricing need checking against Ford Racing Parts.

What You Need to Know

• The R125 is a one-off 1966 Mustang Fastback restomod built for SEMA, not a production vehicle.
• Ford specifies a 347-cubic-inch V8, 360 hp, 400 lb-ft, and a Tremec TKX-600 five-speed.
• Ford has not announced a price for the complete car; the project is a showcase for parts.

Ford’s announcement doesn’t establish how this particular build drives, stops, or holds up in traffic, and we have not driven it. Anyone planning a similar project should price the whole conversion rather than just the headline engine and transmission.

Why It’s Cool

The R125 puts the restomod argument on familiar ground. It isn’t asking you to mistake a show car for a showroom car. It shows how a modern gearbox and thoughtful service details can make an old Mustang easier to live with while leaving the driver in charge.