Hi Jason
The vertical Magnums have a 1/8" pipe plug near the oil filter. There were two versions, one at the oil filter adapter and one under the #1 muffler. If you have the plug at the oil filter adapter you can run an automotive type with sending unit and gauge. With this one you will have to supply the feeder voltage to the sending unit so that will be two wires. I think the automotive needs an adapter fitting. You could also run just a warning lamp but the oil sensor only switches at about 5 PSI. Magnums can run 'normal' pressures of 20-50 PSI.
If the pipe plug is under the muffler the heat will take out the wiring and sending unit so a mechanical type is called for, with a pressure line running to the gauge. My Magnum has this type in a hot spot. I'll be adding the gauge to the dash on my Cub.
The mechanical is simpler than trying to fab up a heat shield to protect the wiring and body of the electric. Of course, with a custom header do what you want. Both have lighted dials (if you wire it).
Both types are available at O'Reilly's. I'm getting the 2" mechanical type for $19.95. The electric is a little more. Either with black or white face, black or chrome ring.
Ted