Which MSD box should I choose for a distributor engine: 5520, 6425 (6AL) or 6530 (6AL-2)?

(1) 5520 Street Fire: the bestseller, ideal for boosting the ignition to the maximum with a strong spark. (2) 6425 Digital 6AL: race edition with rev limiter, ideal if you use the engine near the rev limit for long periods. (3) 6530 Programmable 6AL-2: adds the ability to control timing retard according to RPM or boost, without removing the distributor. Note: if the engine uses two separate ignition signals from the ECU (wasted-spark), these boxes cannot control the timing advance.