(from page 10 of the 1972 Collection)
The 1972, Mustang R-code 275hp (at 5400rpm), 351 cubic inch, 4 barrel, High Output, Ram Air Induction V8 engine. According to the VIN of this car, an H-code 351ci engine came with this car. Also according to the VIN this is not an original Mach 1.
(from page 11 of the 1972 Collection)
Another view of the R-code, 351ci, Cleveland, Ram Air, High Output, V8 engine.