Cosmetic only, the units have cases, wiring, and covers that are exact duplicates of the originals. There are no internal electronics: the wires loop inside to allow the car to run normally without the rev-limit function. Original internals can be swapped into the case to make it functional. Two part numbers are offered: 12450-4A stamped D0ZF-B (6,150 rpm for ’70 Boss 302 and ’71 Boss 351) and 12450-4B stamped D0ZF-A (’70 Boss 429 and ’71 SCJ). Both retail for $449.95. For more information, contact your nearest National Parts Depot warehouse: Florida, 800/874-7595; Michigan, 800/521-6104; North Carolina, 800/368-6451; California, 800/235-3445.