How many are running factory efi on your magnum swap?

Yes. The SCT tuners work fine for the factory Magnum engine PCM. If you are running a completely stock engine, you don't need the tuner at all, but it can still help squeeze a little more power out of it. Best idea is to get a game plan, what you want for power and what parts you plan to run, and discuss your options with the guys that provide the tunes. They can usually help ensure the component colection is not off base for a fuel injected setup. Once settled on a tuning shop and parts combination, buy the tuner (hand held box) and the tune itself (the actual program) from that shop. Some don't write their own tunes, but still offer the handheld with the tunes from another vendor.