i mounted my MSD 6AL under the battery tray in my hemi powered 572ci hemi air grabber 72 roadrunner.
i also left the stock factory electronic ignition system in their original locations.
i powered the MSD by cutting and splicing them together the brown and blue wire going to the ballast just before it left the factory harness. i then ran MSD power wires low along the cowl and then the frame rail to the box. i also ran the coil power wires along the same route and parallel to the factory harness
you had to look pretty hard to not tell it wasn't powered by the factory ignition system.
i had been asked several times how the hemi motor ran with factory ignition system.