Twanderson

Please bear with me as I'm new to this site. This is only my second Mustang. Both have been 68 coupes. I'm wanting to run 14" magnum wheels on my current car. It has factory disc brakes on front. My prior car, I found out the hard way that all magnum wheels won't work on disc brakes. I got lucky when I found a used set that cleared the calipers. Since I no longer have that car, I don't know what the back spacing on the wheels I found that worked on the front is/was. Does anyone know what measurements I need to look for when I order a new set of 14" magnum wheels? Thank you in advance for any help.