Today I picked up a used MSD box from the local engine builder, for use on a customer's 302. It is a 6ALN box. This is a very very interesting box. The N stands for NASCAR. The bottom plate of the box is a clear plastic type material that allows the track tech inspectors to visual check the inside of the box for suspicious extras. In addition, the connection off the side of the box is a GM style connector so that after a race, the tech folks can pull the box and plug it into a diagnostic machine which will detect the presence of any electronic traction control device additions. Also, there is a separate pigtail that feeds an ignition kill switch which mounts on the steering wheel. In the event the throttle sticks open, the driver hits the switch and shuts off the ignition box, thus turning off the engine. I got a great price onthe box, at under $100, plus a used MSD coil. I will use the "kill" switch as a security/anti-theft device and wire it to a switch hidden in the driver's area. The GM type connector is off it now and I will use weatherpak type connectors or similar, to wire it to the MSD dizzy. Very interesting. The box had an 8400 rpm rev limiter chip in it, but swapped down to 6,000 rpm for my use.