It is not the only 88 Mustang with an engine block heater. That is not how personal stats reports lay out the numbers.
It is the only 88 Mustang hatchback with an engine block heater that also had all of the items above it (LX, hatchback, 5.0L, AOD, 1C paint, FD trim, sunroof, 2.73 LS, and electric mirrors).