Thanks. I don't have a Magnum engine, but do have a Magnum intake, ECU, and wire harness I am considering installing on my 273 to get cheap EFI. Even if I use another ECU, I can use the wiring harness, so the pinout you gave is priceless for that.
I shouldn't be too bad on your 273, but the intake won't work. You'll need to get an EFI intake that will bolt to LA heads, which isn't too hard or costly. You also need a magnum dizzy, a magnum flywheel, and to notch your bell housing for the crank position sensor. All in all though it won't be too much.