MSD 6T???

As far as I can see the MSD 6T box don't have a build in rev limiter, but the MSD 6AL have.

Info taken from MSD's homepage: http://www.msdignition.com

MSD 6T:
Even in the harshest conditions, the 6T Ignition Controls deliver race winning performance!To withstand severe jolts and vibrations of harsh racing, the 6T's capacitor and transformer receive additional bracing for a solid mount. All of the circuits and components then receive an extra thick coating of Humi-Seal adding even more vibration protection. Top it all off with a set of sturdy vibration mounts and you have one of the toughest ignitions offered!

MSD 6A:
The MSD 6A is the base model of the capacitive multiple spark discharge 6 Series design. Whether you have a powerful street machine, hard working truck or trick street rod, the powerful multiple sparks of the MSD 6A will ensure complete combustion. Benefits such as quicker ETs, easier starting, reduced plug fouling, more power and even increased fuel economy can be expected with the 6A's high energy multiple sparks. Like all of the MSD 6 Series Ignitions, the 6A will work with virtually any vehicle as long as it has a 12-18 volt electrical system. It can be triggered using breaker points, a magnetic pick-up or the output of an electronic amplifier. All necessary parts and wiring instructions are included (OBD II legal on '03 and older vehicles).

MSD 6AL:
The 6AL shares the same proven circuitry of the 6A with the addition of a built-in adjustable rev limiter. The combination of powerful sparks with the safety of a Soft Touch Rev Control is what makes the 6AL the most popular ignition control in the world.
MSD first developed the Soft Touch rev control to prevent overrev damage to your motor in the event of a missed shift or driveline failure. The rpm limit is adjustable in 100 rpm increments with MSD’s plug-in modules. When the engine reaches your selected limit, the Soft Touch circuitry begins dropping the spark to various cylinders. On the next cycle, these plugs are fired again to prevent fuel from loading up in the cylinder. The result is a smooth and accurate limiting action without backfires or roughness.
The Soft Touch Rev Control also opens the door for you to add rpm accessories such as a Two Step Rev Control. A Two Step allows you to set two rpm limits, one for a holeshot rpm and another for overrev protection.
The 6AL is supplied with rubber shock mounts and modules for 3,000, 6,000, 7,000 and 8,000 rpm.

/Rolf